I've run bb7s on several mtbs for 16 years, and a set of XT Hydros for the past 4 years on one bike. These are likely very similar in reliability and feel to the newer Deore.
I run compressionless brake housing with the BB7s, which makes a huge difference. Opinions of BB7 performance based on experience using something besides compressionless brake housing are worthless, IMO. I have always used Jagwire Ripcord, I think they are now called Mountain/Road Pro.
My take:
In terms of shear performance on the trail, the XT are better. Smoother, more solid feeling, more powerful, and easier to control. BUT not by a whole lot. Enough difference that I appreciate it on a bike that I ride in demanding and technical situations. However, for a road, gravel, cargo, or commuter bike, the BB7s would be just as satisfactory to me.
In terms of maintenance and reliability, I think it is a mixed bag. BB7s take regular tweaking of the adjuster knobs on the pads as the pads wear down. This is frequent, but quick and straight forward.
My experience with hydros (mine and my those of my riding buddies) is the opposite. For the most part they are self adjusting, and between pad changes (which I have never needed to do a bleed for) you will likely never need to even think about them..... until you do. When I DO have issues with my XTs, it can be a lot more work to track down where the air bubble is and bleed it out. If the bubble is in the caliper, I have the take the damn thing off the bike to bleed it.
So for me, the total maintenance is a wash between the two, the difference being that the bb7s are always a quick and easy fix.
I'll put it this way: In all the years running bb7s I never once missed a ride because of them. I have missed several rides due to needing to bleed my XTs.
So my takeaway from this is that for my high-end All-Mountain bike, it is worth it to me to run the XT hydros. But for my new road bike build, I am going with BB7s. I would also go with mechanicals for any disc bike for touring, commuting, or cargo bike.
Others will offer different opinions for sure.
Last edited by Kapusta; 02-18-17 at 09:05 PM.