During the last two days I tried to download one of the Windows 10 Technical Preview ISOs, a file of roughly 3GB size. I actually tried four times, never ended up with a download that matched the SHA-1 given by Microsoft, in fact all downloads had a ‘unique’, non-matching SHA-1. Same happened when I tried to download a different ISO.
I then replaced the RB951 with a Cisco RV220W - and guess what: Not only was the download roughly 4 times as fast, it also featured the correct SHA-1.
Same was true with any other ISO I subsequently downloaded: RB951 all fails, RV220W all success!
I then, out of curiosity, used the el-cheapo router provided by my ISP: The ISO download I tried with that one also was flawless.
As for the RB951, it’s actually a RB951Ui-2HnD. During my first attempts to obtain those ISOs, the RB951 ran ROS 6.19, but I gave ROS 6.20 a try since yesterday. The RB-951 setup is really simple: Just the defaults that came with the device, plus a port forwarding rule for a web server added. The downloading client computer was attached to the RB951 by LAN cable.