Form the sound of things, if these can actually handle 50A, the app works for the most part, and it successfully manages your batteries (balances correctly, high/low cutoff, etc)... that is a damn good price. I'd be skeptical at that price if I was trying to run anything close to 50A... but you never know. I've been looking for a good smart BMS with adjustable high/low voltage cutoffs, and adjustable balance voltage... everything else would just be a bonus (again, a quality BMS that handles everything it's supposed to correctly, that is reliable for at least as long as the batteries in the pack are viable to use). I grabbed a few bestechpower BMS's recently... I honestly could not get a recommendation for any other BMS from anyone, it was them, or a no name chinese crap shoot... but they did not have any smart BMSes in stock, and I was told an extremely high price for them when they did come back in stock (though it was a ballpark... but still close to 4 times the price of one of these).
I did buy a Cycle Satiator, so it can handle setting the max charge voltage, etc... but I would prefer having a BMS where I could select exactly what want (adjust quickly for the occasional trip outside of my normal ones), and just not have to worry, and not have to depend on a $300 charger to be able to charge to 80%-90% normally.
Keep us updated on your experience... I am tempted to grab one just to try it out at this price.