Re:
Good, good brakes. But not better than M395s...just lighter.
The main thing for Rxs is they are very light - but they are costly if anything needs replacing (seals, clamps etc). Advantage is if you're running SRAM you can get a matchmaker clamp and fit shifters and brake to it - they are fragile tho.
Rxs are also tiny and have much modulation and when set up well on a light bike, stop quick. I wouldn't use them for heavy full-sus tho.
M395s have less modulation but equal stopping power, and are easy to upgrade the calipers or pads, they also in my experience never fade. Shimano's Deores always squeal like mad, XT are great.
If you want to reduce size & weight; J&L Superlights are effing brilliant, better made than Formula, and that counts for a lot in terms of feeling secure on the bike when you need to haul on them.