This won't be a the best review since I've only been learning bass 6 months so far, but I'll do my best.
Got the MB500 on Thursday and was playing it through my ATH-M50s and it sounded great at all the recommended settings in the manual. No hiss, no fan noise. Reacts nicely to different picking styles, fingers/thumb/slap/pick and growls when you dig in. Just seems very versatile and easy to get a good sound out of no matter what you do, which is great for a noob like me.
Got to play the TB153 on Sunday. I wanted the flat pack kit, but it got to spendy for my limited budget, plus after not having any amp or cab this whole time, I just wanted to plug in to something. While cab shopping, I hated every 15 inch cab I played through. They all sounded muddy or like they had a blanket over them. Not tight or defined at all. I played a few 210s and 410s and was originally going to get a 410MBE. I decided to take the plunge though since all the fearful reviews talked about a tight defined tone, which is what I want.
The sound I got from this combo was exactly what I had in my head. Clean, punchy, and defined without too much of anything. Dispersion was great. I play in a 2 car garage with a high ceiling and pretty reflective walls, but it sounded great and even no matter what side of the cab I stood on, including behind. It's kinda big and heavy, but overall not bad to move. I just bear hug it and it's fine.
In the end, it was worth the wait to save up and get this stuff right off instead of buying something cheap to start off on. I really want to play this gear as much as I can and I would definitely buy both over again. I'll try and remember to record something next weekend to give some sound samples. If there's any questions anyone has about this stuff, I'll do my best to answer.