I have to put my hand up as having gone through the route Z240 - Retra ProX - Retra ProMax.
I’ve never regretted for a second the move from Inon to Retra. I loved the Z240s but the Retras are way ahead in terms of power, ergonomics, build quality, functionality, light quality, accessories.
I moved to the ProMax about a year ago. The reduction in size of the additional battery pack was a prime driver. Yes, they are significantly more expensive than the Pro X but value for money is, I think, a bit of a subjective term. I think they’re well worth the cost. I got a pretty decent price for my Pro Xs so was happy to find the extra.
I find the Retra strobe/LSD combination fabulous, their reflector a super bit of kit. I use HSS a lot shooting into the sun. All in all, I’m really happy with what I have and zero buyer’s remorse.
If the price of the Pro Max doesn’t represent VFM for you, how about second hand Pro Xs. They are to be found and I really doubt you’d regret getting them.