I had the exact opposite experience. After already owning a DM42, DM41X, and a DM16L, and I bought a DM12L for a client. The screen had several LCD segments that faintly showed as always on. I wrote an email and was contacted by Michael (the founder) almost immediately. He said they'd happily take it back and send me a new one, but it would take a few weeks for shipping from Europe. Instead he suggested that I first try putting it in the oven at 70C (160F for us 'Mericans) for a few hours. So I disassembled it and put just the PCB/display unit in the oven. And sure enough: problem solved!

tl;dr: I thought their service was great.

Although I do love my real HP's, too. I own maybe a dozen. I think the 32sII is my favorite, but I dearly miss my 41CV from back in the day. Maybe I should find a used one of those.

On the programming side: I definitely agree with those saying calculators were/are an entry to programming. My first programs were on an HP-29c. I thought I had invented binary search!