In my opinion, yes, they are a lot better. Lyman's M expanders have three features I really like.
First, they push into the necks to work rather than expanding while withdrawing as do conventional "button" expanders. This reduces case stretch.
Second, they have a looong expander-to-neck bearing surface. For bottle-neck cartridges this helps them guide straight so finished necks tend to be a bit better aligned.
Third, those expanders have three diameters. The first diameter expands necks to just under bullet diameter, just as a conventional expander does and you may wish to stop with that. The second step is a very short section that it expands mouths to just a bit over bullet diameter so bullets can start smooth, straight and without damage to their base. The third step actually flares, or bells, the mouth if it's needed for seating over-sized lead bullets. The user simply adjusts the expander stem's depth for the degree of expanding he desires.
I have one for ALL of my normally reloaded calibers, pistol and rifle!
