I use various microscope E.Ps. I have had to 'modify' the 30mm barrels to fit the 1.25mm diagonals correctly which are a couple on mm larger. The 'top end' microscope E.P. versions do actually give impressive images -excellent on axis resolution, reasonably flat to edge and with minimal other distortions. Mine display only minor secondary reflections and show good contrast. The FOV is not wide however - about 50 degrees in mine. Currently I have 2x 'W10X's which I use in a binoscope and a 'SW15X' which I use as a general E.P. The W10X equals a 'normal' 25mm E.P and the SW15X is equal to a 16.6mm E.P.
They are worth seeking out and experimenting with - some may have trouble reaching focus. They can however be a very cost effective solution.
[Below is great article that includes the 'maths' for working out the magnification equivalents.]
http://www.cloudynights.com/item.php?item_id=365