Had one for over 5 years, I can only assume you're using it wrong, I have the threads lubed with MOS2 and clean them each time the vice comes off the mill, I have never come close to rounding the hex in the screw, I don't use cheap hex keys though!
In all fairness i am not a newby learning the ropes.
I can only assume times not a concern, time costs money.
Its the allen key supplied thats rounded off. Not a lover of hammering things like to do it by feel but this is a necessity to tighten these vices up with a limited arc of travel to get a hold on the allen key.
Also take it you dont use often else you would know its a ratchet style and cap head bolt has a minimum amount of travel mean while arcing as tightens up. May well find have to back cap head to its max before it unscrews from the block to be able to get in to the next ratchet along which provides more clamping force. Vice versa if on another ratchet it pulls down rather than more against the part!
Has happened a few times by not unscrewing cap head out fully and dropping in a width it cant cope with. To get that, cap head has to be fully unscrewed mean while holding the eccentric cam against spring pressure then starting bolt off 1/2 a rev continuously each time used to get in to another ratchet, tell me i m talking b…..s