I use M2 for edges and Old Pochmann for corners. I’ve been using a number system instead of Speffz for my blind solves in order to make better use of my PAO. The system of using letters just never worked well for me, especially when you have pairs like QK, CK, KC, KQ, etc. which need different words; or pairs like XH which are hard to find words for.
Using the PAO system was slightly inhibited because I needed to memorize in pairs to keep track of parity, so I had to use PO. However, I found this video which explains a way to avoid parity:
The idea is to look at corners and recognize if you have an even or odd number of corner swaps. If it’s odd, you take care of parity during the edge solving by solving UB and UL into their swapped positions, which always gives you an even number of edge swaps.
Thought this might be useful for anyone doing blind solves, your solve becomes more efficient and you aren’t restricted to memorizing in letter (or number) pairs. I’ll definitely be using full PAO for my solves from now on.