My order for the credit-card size DM-15CC has arrrived. It is a neatly finished-off product - and it works ! Someone remarked the display contrast ratio wasn't too good but mine is just fine. The blister keys do have to be pushed quite positively to register. The thingy the bank gave me to access my account online uses much the same plastic blister keyboard and that was stiff at first, but with use it has eased, so perhaps it will with the DM15.
I ran Katie Wasserman's pi programme, it took 5 hours 48 minutes. Katie says the original HP-15C takes 43 hours, so it is 7½ times faster than that, but obviously slower than the LE. (I set it off at 6 p.m. & I was just ready to give up & go to sleep when it got there!)
All in all I'd say not a replacement for the desk top, but so portable it is really handy for those programmes that you enter just once and use with different data when on the move. Like times & wind lay-off in a holding pattern (aircraft).