I have used lots of grandstream products over the years (my very first phone was a GXP2000) from ATA’s (HT206, HT306, HT486, HT466, HT503) and Phones (Budgetone 200, Budetone 201, GXP2000, GXP2020, DP750) and Video Phones (GXV3000, GXV3140, GXV3240, GXV3275) and PBX’s (GXE5024, UCM61XX).
In general they are fairly cheap hardware but unfortunately in my experience not very “hardy” in the long term.
The success story has been the DP750 / DP720 (3) Phones which I have been using for nearly four years, a couple of firmware upgrade issues at the start but since then working well, feel like a decent product and no hardware failures.
Also the UCM61XX didn’t fail, only ever ran two with about three years service between them but no hardware failures and software seemed to work fine (not as flexible as FPBX but usable enough).
After that my grandstream experience has been really poor. Most of the original power supply units went into a bin in under two years, of the HT206, HT306, HT486, HT466, HT503 only the HT503 survives today but with a faulty FXO port that shows busy even when unplugged, all the Budgetone 200, Budetone 201, GXP2000, GXP2020 died either in service or during firmware updates except one GXP2000 which is no longer in service but remains working.
Of the Video Phones, GXV3000 (2) all had screen failures (half the screen went fuzzy) GXV3140 died in service, GXV3275 touch screen stopped responding accurately and while both GXV3240 I have still work they have become very ‘clunky’ and have need a reset to try and speed them up more than once.
The GXE5024 was sold working but I really struggled to keep trunk registrations up on it despite FPBX and 3CX systems behind the same routers having no issues doing so while I had it on test.
I have installed a couple of Sangoma pbxact appliances without issue, and although I don’t maintain them I understand they remain working fine, others I know who have had more to do the pbxact appliances speak well of them and don’t report any failures.
So from my personal experience and feed back from people I trust I would say the reason for the Grandstream products being cheap is because they are, and the reason the pbxact appliance is expensive is because it reflects the quality (and therefore longevity) of the product.
I know I would rather trust a pbxact product over a grandstream one as my PBX, especially in a commercial environment where downtime is lost money.
On a final note to be fair to Grandstream the DP750 / DP720 experience I have had suggests their quality is much improved, but outside of the UCM61XX I think I would avoid their legacy product and only use a UCM61xx in limited circumstances (home use etc).