Hi there, its been a while since I was on here. I have had a number of OTS amps. The current one was built by a local electronics  tech here in Australia and I was able to specify some things I wanted in the build and lead dress after having had a few of these amps in the past.

I have had some components changed out by another "D" style enthusiast and also some value changes in my search for my ideal dumble tone.

I mention this only to illustrate that what one may find is an improvement is only so in relation to that persons particular end goal. As such and for me, the change to MM transformers was a good move. The amp is a step more articulate with the MM transformers than the stock ones for me and my ears.

The power transformer was not changed as my tech measured the values and sag etc and said it wasnt worth changing it out. However the output and choke were changed out.

The difference is a matter of degree and how much the single percentage points gain is worth to you. The two biggest differences I found are,

1. There seems to be better control over gain levels with pick attack alone.
2. There seems to be an improvement in overall clarity of notes and definition with chordal work.

my 2c

I haven't done any comparisons, but I installed MM's in my Bluesmaster 50 and it sounds fantastic.