The first thing I recommend to the buyer of a 500 EL/M or any of the later models with the Palpas anti-reflective coatings is to treat them with that Aerospace 303 stuff. It keeps the cracking from getting any worse. I have no idea why Has had to introduce that stuff and not really do their homework first.
I have both a 503CW and the 500 EL/M and aside from the size, the 500 EL/M is quite handy! With today's 9V battery adaptors, they perform quite well. One thing to be cautious of is the battery compartment latch. They can be damaged easily and then you need to call Hassy in NY to send you a replacement latch--nearly $40! But it does save a nice EL/M.