I searched, this question is probably somewhere, but searching for z stick pro got nada
money not top issue, but reliability and compatibility is.
I used to recommend a 2-in-one dongle (the HUSBZB-1 GoControl/Nortek) stick and they do work. But as the two different protocols advance at different rates it's harder to upgrade the hardware when you do that. If you're space constrained, then go for it. But if you've got the free USB ports, I would recommend separate devices on some USB extender cables as you can upgrade them independently and on the cables you can separate the radios some and also get the a little further from the system.
I hear you. Thinking about it, I was assuming that there were 2 "drivers"" for the dual dongle, but most likely its one driver. Significantly more money, but yes, less danger of getting in a spot where an upgrade "breaks" one half of the dual dongle.
I was also concerned about performance, where 2 individual devices could execute commands faster or with "less confilict" than a single USB device as the gatekeeper to the 2 functions.
I'm making an assumption here as I don't have one of these devices, but it probably operates similar to the HUSBZB-1. It probably presents two serial devices to the system and both are accessible at the same time. With the Nortek device I did occasionally see where one side had issues but the other side functioned just fine. Both sides had separate firmware drivers for control that were independently upgradeable, it's likely the same for the Z Stick Pro