The Maestro Echoplex is an analog and vintage echo box. This isn't your typical piece of outboard gear, but it does have 1/4 inch connections for input, output, and the foot switch. This isn't rack mountable at all as it stays in its own box.
In terms of parameters and setting up your sounds, the Maestro Echoplex is fairly easy to get used to. The unit has knobs for sustain and echo volume, and also has a large slider for echo delay, ranging from 0 to 35. As you can tell it doesn't have a plethora of parameters, but it definitely has enough to get the job done in my opinion. The manual is pretty detailed, so if you feel that you might have trouble setting this up and using it, I'd recommend consulting the manual.
I haven't used all too many delay boxes other than this one and the Roland Space Echo, but if the Space Echo is the holy grail of units like this, then I believe that the Maestro Echoplex would come in second. While definitely not as versatile and great sounding as the Space Echo, this has a lot of cool qualities about its sound and is a great unit in its own right. I've only had the chance to use this on a few occasions for throwing some echo a lead vocal and was very impressed with the sounds that I was able to get. I found it to be great for both subtle slap back delay and for more echo and wetness in a delay. It definitely has a warm and realistic tone...
Other than the one that I have used, I haven't seen any other Echoplexs around. They can definitely be found on eBay, as there are always a lot of them up. I would imagine that some studios have them, but this isn't a main stay by any stretch. The price of these does vary used, but can get pretty expensive. Unless you're looking for a true analog echo and have a large studio, it is probably more realistic to check out a more compact unit, or a plug-in, but there definitely aren't too many legit replacements for a unit like the Maestro Echoplex.