Does web caching really improve internet quality (web surfing)?
How long does it need for web caching to show real improvement?

I have tried some time to test web proxy but customers always complained.

cache system correctly configured increase the performance.

research on the forum about this.

regards

is it mikrotik proxy or external proxy?

It depends on what you are more familiar with.
I prefer external Squid proxy in a Debian based host. In the other hand though, i have read very good scores for the new MikroTik proxy.
You have to test, and test, before you start to be familiar with any of the types, and then choose the best for you. Remember to give the proxy time to fill the cache.

If you post the config here it may be more simple for us to give you some clues on what to choose