Absolutely explody batteries. Should be well matched, so individual cells won't run away from the others, at least initially.
Some day, I assume they will. Your system lacks the cooling designed by Tesla to ensure a runaway cells doesn't ignite all its neighbors.
If you want to operate without BMS, I suggest you put batteries in an "ammo dump" outside your house.
I certainly recommend a BMS. You regulate overall voltage, but you have no control over individual cell voltages when they diverge. Recipe for ?