The PlayGo does look nice. I saw Taki Udon's video about the color temperature being better than on the Go-Play 2 models he'd been playing on. I'd probably go for it if the 350 wasn't an option. As it stands, I'm more likely to get the Odroid Go Advance since, when it's in stock, a single unit is about the same price as the PlayGo ($75 shipped to my location) and the rockchip is robust enough for N64, Dreamcast, and PSP. (They are in stock right now.)
Really loving the 350m, though. I'm still on the stock FW and the battery life is more than enough for the amount I'm likely the play on a given day. It feels incredibly solid. The build quality is on par with, or better than, my GPH consoles. Some have compared the build quality to modern Nintendo, and they may be right. YMMV, but mine seems that good. I'm not sure I'm going to rush to crack it open to install those custom buttons. I don't want to mess up a good thing.
Mine shipped with pcsx4all 2.4 (Compiled 3-12-2020) and runs at a stable 60fps for most games. I was very pleased to find that it supports .pbp compressed images.
If Dreamcast, N64, and PSP aren't dealbreakers for you, I'd say go for it. Maybe find a seller that will ship it in fewer than 2 months, though.