Is the Hassie 500EL the 'stepchild' of the Hassie family? Why do these bodies seem to be cheaper than all the rest? Is it because of that battery issue where you need an adapter to run it on a 9v battery?
The 500EL doesn't have user interchangeable viewing screens. This important feature was added to the 500ELM. The early screens have a reputation for not being especially easy to focus. Usually described as "dark", I find it more a lack of contrast or something. With an ELM, you have the option of easily trying different screens. If you are young with fine eyesight, you may not have any difficulty with the EL screen. Different screens can be installed in an EL, but it isn't considered a DIY project.
The motorized bodies in general aren't as popular as the mechanical bodies. They are heavier and bulkier. In the studio on a tripod they are great. Packing them around in the field isn't as much fun as a 500CM.
The 500EL is the oldest motorized series, so it is easy to generalize that they may be more apt to have "problems" of some sort. Obviously a later ELM or ELX may have had considerable more use and be closer to "problems", but that isn't they way most folks think. Possibly parts aren't available for the EL series, but I don't know anything about that. Hopefully someone can comment on that issue.
I bought a 500ELX off eBay a few years ago mostly because I wanted to play with a motorized Hasselblad. And it is a way cool camera. Sort of magic the way it advances the film. I guess I'm easily entertained. I got it with bad batteries and bought a 9V adapter off eBay. It has been working fine ever since. But I don't use it a lot, preferring the 500CM. After buying the 9V adapter, I found an online article on DIY adapter. Had I known how easy it was to make, I would have done that.
I haven't been following eBay prices on EL and ELM bodies, so have no idea the price difference between the two. Myself, I would pay more to get an ELM or ELX, although I'm not sure how much more.
It made more sense when 70mm film was available so one did not have to reload so often.
Warning!! Handling a Hasselblad can be harmful to your financial well being!
Nothing beats a great piece of glass!
I leave the digital work for the urologists and proctologists.