For the last 5 years, I've been trying solder-your-own calculator kits. The easiest ones are usually basic algebraic calcs with limited functions. But in this case, I ordered the HP-41 variant and was very impressed. I've never owned a true HP41 but I knew how powerful they are. This kit combines the function catalog and keystroke programmability of the HP41 with an extraordinarily well designed through-hole PCB. I had the soldering done in under two hours with only one mishap caused by my impatience when I bent a lead on one of the tactile keys. The component spacing and clear labeling printed front-side made soldering child's play. The kit worked correctly as soon as I inserted a new battery. If you have the enclosure and overlay, finished product looks very nice and can be pocketed without fear of damaging anything. If not, there is still a very attractive PCB with printed key labels and rubber feet so it will rest on your desk without wobbling. The backlit display is a real delight. So, you don't have to sacrifice power for ease of assembly. You could teach a middle-school or high-schooler to solder with this kit and then teach them the power of RPN on a classic device with a rich history and readily available programs found on the internet.
I've wanted an HP-16C for years but never been able to afford one. The other versions seem to pop up on auction sites regularly at fairly reasonable prices but not so the programmer's version. As soon as I saw this, I ordered it. Delivery from the USA to UK took about a week, much quicker than I expected. I built the calculator in less than an hour and it worked as soon as I switched it on. I managed to have the original HP manual printed using an online service which cost me £8.53 (UK prices) including postage. This was much less than I could buy a used manual from an auction site. Now I have the manual, I can try to learn RPN and put the calculator to some serious use. I asked a few questions to "HobbyStone" before placing my order and they were answered very quickly, something I really appreciate. I'm absolutely thrilled to finally own something that I've lusted after for years.