Specifically this one, seems to be super human!
XS+2733LC15D
https://mikrotik.com/product/xs_2733lc15d

Do I have this right, its a BIdi SM module that can negotiate speeds including
1.25 / 10 / 25 up to 15K..........
Funny distance as most vendors will state, 10, 20, 40K as standard distances. I wonder if tis a 20K but for conservative purposes stating 15K.

if so pretty decent for $349 US.

How does this compare for example.........
https://www.fs.com/products/140501.html ... &id=289399 $164x2 = $328 US
Its not clear if this model is also 1.25 / 10 compatible ? Can we assume that??

From my readings, it appears that SFP28 modules will work in an SFP+ housing (but only reach a speed of 10gigs) and vice versa (noting that an sfP+ module is maxed out at 10) having the same pin out construct.
The conclusion is that for some reason the MT module will work in an SFP housing 1.25 but everywhere I read that is not possible?? (even an SFP+ will not work if stuck in an SFP housing)??

Thus two questions.......

What makes no sense to me is why 25gigs. I see 10gig switches are very common now and 40 gig switches being noted in more models so what is the point on buying modules rated to 25gigs?? SFP28 ?????

How can the MT module be both sfp28 and 1.25 (sfp) compatible ?

Specifically this one, seems to be super human!
XS+2733LC15D
https://mikrotik.com/product/xs_2733lc15d

If Normis tries to sell you the very pair form picture on propaganda page, you'll be hosed ... because they are cloned (same wavelength which doesn't work well for BiDi, same serial number) ...

Do I have this right, its a BIdi SM module that can negotiate speeds including
1.25 / 10 / 25 up to 15K..........

Seems like it.

Funny distance as most vendors will state, 10, 20, 40K as standard distances. I wonder if tis a 20K but for conservative purposes stating 15K.

I'm not sure how other BiDi modules fare regarding distance. If you compare that to distances for "straight" (fibre pair) SFPs, then BiDi includes a filter which separates both wavelengths so that correct wavelength hits receiver and receiver is not saturated by transmitter (most receivers are actually wide-band receivers and optical element has to filter out all unwanted wavelengths). Each filter adds some attenuation (read: reduces range), only some are better than others.
OTOH, there's the matter of Tx power budget v.s. sensitivity and it's easy to loose a dB or two in overall power budget (15 km is 1.25 dB less than 20km).

How does this compare for example.........
https://www.fs.com/products/140501.html ... &id=289399

Not sure if specifications on this page are complete, but if they are, then this module can indeed reach longer distances because it's got more powerful transmitter (6dBm vs. 2dBm on MT module). At the same time receiver sensitivity of FS module is a tad better than MT's (-14 dBm v.s. -13 dBm). Both are most probably able to run at extremely short distances (long distance SFPs are not because transmitter can not use power low enough not to saturate the receiver). FS module is also certified as "industrial temperature range" which comes with some price increase (normal temperature range is 0°C-70°C and that's SFP cage temperature ... probably what most MT devices report as SFP temperature). The low temperature is important for running equipment outside ... if during winter time there's blackout and equipment cools down.

Its not clear if this model is also 1.25 / 10 compatible ? Can we assume that??

I'd rather not. FS doesn't explicitly state that module supports 10Gbps sync rate, they only state SFP28 compatibility.
But then ... why would you want to run at slower speeds? Fibre connections don't benefit a longer range if line rate is decreased. If you have SFP modules at both ends that can synchronize at 10Gbps, then let them run at that speed. Surely you need devices which support SFP+ or SFP28. If you don't have that, then it's much cheaper to go with good ole SFP (1Gbps) modules.

My (limited) experience is that modules may synchronize at speeds exceeding SFP port rate. E.g. if SFP+ modules are plugged in SFP port, then device<->SFP obviously works at 1Gbps ... but synchronization rate over optical fibres can still be 10Gbps.

From my readings, it appears that SFP28 modules will work in an SFP+ housing (but only reach a speed of 10gigs) and vice versa (noting that an sfP+ module is maxed out at 10) having the same pin out construct.

Some articles (like this one) support your theory.

What makes no sense to me is why 25gigs. I see 10gig switches are very common now and 40 gig switches being noted in more models so what is the point on buying modules rated to 25gigs?? SFP28 ?????

When they practically reached 10Gbps speed, they had two ways forward ... some felt that 40Gbps by utilizing 4 fibres (10Gbps each) is the way forward. Others felt that single fibre, but using advanced transmission techniques is the way forward - this produced 25Gbps standard. BTW, 100Gbps is again achieved either by using SFP-DD (2 fibres) or QSFP-DD (8 fibres).

How can the MT module be both sfp28 and 1.25 (sfp) compatible ?

It seems that electronics part of module is a tad more versatile than in FS module. Electrically and physically SFP/SFP+/SFP28 modules are compatible and if electronics in SFP module is versatile enough, it can talk to host device with either of these protocols. And some others, like CPRI or FC.

Well seeing the plethora of 25Gig managed switches, I dont think I will be buying the more expensive SPF28 modules and will stick to those that can handle both SFP and SFP+
Looking for a Bidi Module for 1.25 and 10gig (that will do SFP and SFP+)
Guess what they dont seem to exist?

No, they don't. 1000BASE-BX & 10GBASE-BX use different wavelengths.

Hi there, then explain to me how the product I noted at the top [ XS+2733LC15D ] can DO ALL THREE!! 1.25/10/25.
In fact how come it calls them SFP+ transceivers and yet it can do 25gigs, which is SFP28 standard??

Call me confused!!