this is IMO the single biggest benefit of external balancing. I can often fit a whole nother P or S group by ditching the BMS. untill they get tiny like the Flexi. even that takes up some space, and often my builds have zero space left over.
I do charge through the balance leads, and there is a bit of bias but no more than a few hundreths of a volt when I checked manually. gone about 800 miles on that board and the cells still perform well and balance within .03v.
It’s not cheaper than a brick charger for the first battery, but you can have several battery configurations and charge with the same charger. I have 5s packs in a 10s board, and 6s packs in a 12s board and charge them both from the same charger (different plugs though). The 6s scooter also charges on the Imax.
I put my switches between the two halves to separate them. when separated, they can be charged on a duo charger, but if you forget, poof. so now I only ever charge one half at a time out of an abundance of caution and lack of working duo chargers 
needless to say, if I build a battery for someone else’s go-go- gadget, it gets a BMS and brick charger on delivery unless they say otherwise.