I'm a pumper, well I have tried it before and now do it once a week with the routine I'm on.
Pumping is really strange for someone starting out. If you pump you are someone who likes to enjoy pe. Like a hanger is a hard worker, pumping is really a lot more fun. I have seen gains with pumping but only temporary. IRS usually water build up through high preasure.
Your husband is probably mistaking erection improvement when pumping in the tube for that extra half an inch, possibly try asking him to wear a cock ring post pump, this might help with the pumping enhancement, though possibly you need to be delicate when asking. He might be really happy with what he believes he has gained, don't ruin it for him.