A rigid MTB will go anywhere and do almost anything. MTB's whether rigid or sprung are designed for very harsh conditions. I raced for 4 years in Northern California at the end of the Klunker era and beginning of NORBA. All the race bicycles were unsprung. They were very fast. However the rider takes a beating at race speeds. Bleeding kidneys are not uncommon after a particularly rocky course. I found that I was no faster and finished no better on a derailleur equipped bicycle as opposed to a single speed. I raced bicycles that were equipped with coaster brakes and Mafac cantilever tandem brakes on the front fork. I raced bikes with cantilever brakes on both wheels. Frankly the coaster rear brake worked fine as long as you didn't use it for a drag brake. I would lock the rear wheel for a while until the bike started slewing around then unlock. This keeps the brake from overheating and usually provided the necessary speed reduction. Many downhills were so steep that the front brake needed to be used at times. This brings us to the other problem with rigid bikes. Basically going downhill at speed meant not grabbing the handlebar grips at all. I would ring the bars with my forefinger and thumb on each hand and push the bar instead of pulling it. The moment you grabbed the front brake you became one with the tremendous beating going on and you now couldn't see much of anything because your head and eyes were vibrating up and down so hard. After I quit racing I rode rigid MTB in the Sierra's a lot and really enjoyed it. I didn't have to go fast downhill like I did racing so a rigid bike is fine for casual rides. Now days I would opt for a full suspension bike with lockouts on both end suspension units. Suspension really shines going downhill. It mainly sucks energy the rest of the time and is usually not needed. That said I limit my offroad these days to gravel/dirt roads and easy trails. No more Downieville downhill or Tahoe rim trail. I'm getting too old for the beating.