The Retron 5 did indeed release, but from the sounds of it, Hyperkin didn't release nearly enough to meet preorders. I preordered through a local store and I'm still awaiting fulfillment on the gray console. The black console won't be released until September, maybe..but that was only announced within the last few weeks, I think. Maybe around the time they raised the price by $40?
It can kinda be considered vapourware, though, maybe, because I think the Retron 4 that was never released just sort of morphed into the Retron 5 after that one was delayed for nearly a year, too.
That model is on their list of fully compatible models: BEFSR41 (v3) 1.04.8, 1.05.00 Those numbers after are the supported firmware versions so make sure you have that up to date. You should be able to get an open NAT with that model no problem.