There are reports on Hpmuseum.org about Primes freezing with the last firmware version. Admittedly, I have used my sample (latest version, G8X92AA) mainly for arithmetic calculations, and therefore I’m not pushing it to the limit; but the previous model ( NW280AA ) failed several times with the latest firmware. If anything, the last model seems to be more stable.
On the other hand, by perusing the HPmuseum site, I see that people is having problems to find the latest model in the US. Unfortunately, I would recommend them to wait until it is available there. The transport prices and current post regulations make it very inconvenient for both seller and buyer to send the calculator overseas; moreover, as it is an EAME model, the guarantee will not be valid in the US.
Same applies for the rest of EAME calculators, by the way. And it is a PITA, since the guarantee covers 2 full years - way ahead of the typical 90 days cover you can find elsewhere. And it works! I have had to call for guarantee twice for different devices (you can bet that I have all of them and use them quite often). I received immediately (in three or four days) a new, identical calculator, packed in bubble wrap (as opposed to a proper blister), but anyway it solved my problem. Hope it solves yours too. I often get calls of our customers asking for help in that regard, and the best advice is to go directly to HP’s help desk for calculators.