It all depends on what you want to do with it. Just as important as the engine, is the complete power package. (Engine, tranny, gearing, turbo?...)
The _majority_ of school busses are ordered with power packages to work great for pick up/drop off use. This means that they are designed to handled lots of stop and go, low speed, short trips on level roads. They are (generally) fantastic for that. Some top-out as low as 45mph max. However, if you are looking to add a lot of creature comforts (read:extra weight), maybe a towed vehicle (a toad), long highway road trips, and/or steep grades it is really important to consider what that "super reliable engine" is paired up with. If the transmission and vehicle weight are not appropriate for your needs AND the engines capabilities, it will never be the right engine for your intended use, and you will kill your engine and/or burn up your transmission in short order, or be traveling at a slow and steady pace for a long time.
Activity busses are generally geared for highway road trips with bigger engines and trannies FYI.
I am not an expert on engines by any means, but I have read a lot of positive info about that engine, but also lots of complaints when it is paired with a heavy/big bus and less powerful transmissions.
Use the search feature in the forums and look for "power packages", or just the engine and or tranny you are considering. You will likely find lots of info.
Good luck! And welcome!