That warning is out of date and now incorrect. It did apply to all OBi devices, not only those sold by Amazon UK. However, OBi devices do still support Google Voice though it may be necessary (and in any case advisable) to update the firmware. There has been no hardware change to OBi devices necessary to continue working with GV.
But, and it may be a significant "but" for anyone outside the USA wishing to use GV, if you do not have GV numbers obtaining each one requires that you have a US phone number that can receive incoming calls and has not been previously used to get a GV number. This is purely a GV requirement, nothing to do with using an OBi device. The process of obtaining a GV number does not require the use of an OBi so you may wish to try that before committing to a purchase.
If you do not plan to use GV you can confidently purchase an OBi202 or other OBi ATA from Amazon UK. The only difference between one from there and one purchased in the US is the supplied power adaptor fits the UK style 3 pin mains socket.