I've got the (original) Apeks Tech Shorts and the OnSub Tech Shorts side by side right now. Both brand new. The difference is pretty obvious in most places.
Apeks shorts have a grippy bum, whilst the OnSub ones have the same pattern and look similar, but it's nowhere near as grippy.
Apeks pocket side velcro is 'normal' velcro, whilst the OnSub ones are that micro velcro stuff that's REALLY hard to get open - there's no way I'd be able to open those in thick gloves. It's very hard to expand the pockets with bare fingers and brute strength.
Rubber seams on the apeks are just neater and look better applied.
Stitching looks to be about the same.
It's bad enough on the OnSub ones that I've requested a return and refund. :/
I'd really suggest if you want those particular shorts, get the genuine ones (although finding the original model which I prefer for the velcro on the pockets for when you're diving with little in the pockets to keep them more streamlined, does prove difficult now).
Can upload side by side photos if anyone is interested.