Thankfully, they are not TOO popular. In fact, many of the bothies that were too popular have since disappeared as they were being frequented by folk who didn’t really appreciate what they were for, would turn up with massive amounts of booze and would burn everything in sight while leaving them in a mess. Those that remain are largely in remote locations. For many years, the SMBA kept the locations secret. That’s no longer the case as the internet has made it a bit futile. As you never know how full they will be when you get there, having some form of alternative accommodation is sensible although it obviously takes away one of the benefits. Weekends and Bank Holidays in the summer can see them being very full. Midweek winter nights they’ll mostly be empty. You also need to be sociable enough to get on with a bunch of strangers, but that’s half the fun. If you don’t have too far to travel, taking in some fuel for a fire is common.