I’ve used BIAB for many years and I really love it. I mainly use it for Jazz and folk music. I think for more mainstream music (Jazz and Rock) it’s great. On the other hand, for folk music I have a bit more trouble finding a style that I like, as most of them are too “busy”. They seem to be missing some basic accompaniments. For example, i’d like a simple Down Up Down strum for jigs & reels, but the realtracks are very busy with complex rhythms that trip me up. That’s the first reason I wanted to try the Beat Buddy.
The second reason is that I like to do some improvisations with a drone, and controlling fills and changing the pattern from A to B variations whenever i want is nice.
The downside to BIAB, other than busy styles, is that everything has to be planned out in advance. The bars for the verse, chorus, how many repeats, etc. And the format is not very flexible. This is why it’s great for jazz, but less good for pop. If you want to stop the drums, have a quiet bridge, for example… it can’t. YOu can export the audio into a DAW and do as you wish, if you’re up for that.
So for me and my use, they’re very different. I haven’t yet tried using BIAB with beat buddy, I think that would work with the midi sync.
Overall if you need bass then BIAB would be good if you can except the limitations I mentioned above. I think beat buddy is better if you either have people doing accompaniments (guitar, bass, etc.) OR if you don’t need it (you’re playing guitar and don’t need bass or playing with a drone).
BIAB has a huge sale every year in December. That’s when I do my upgrades, and not every year.