I have to agree that marks aren't something I'd want...I tried using the Putter Pal and it totally messed up putting to the point I turned it off and let it expire without using it for more than a round.
If you want a mark, there are plenty of ways to get them yourself. There are forum posts that have the image of the distance marks for different putters. Take a sticky note or a piece of tape and measure the meter on your screen, mark the tape or post-it and viola - there are your marks.
I agree, also with CP, that marks are just another thing to complain about and doesn't contribute to the "real" aspect of the game. Even with the marks, there's going to be variation in shots anyway (wind, elevation, spin).
(I'm of no opinion on the mulligans option, FWIW.)