I'm one of those who swear by them
Where I live, it's hot and humid most of the year, which means no jackets or sweaters, and usually I have to have a holster that will work with a tucked-in shirt. Pager Pal does what they say it does--keeps my MK9 concealed and available.
And, I find it to be comfortable--but that's only after wearing it a while. At first it was quite stiff and inflexible, but after a while the "pancake" conformed and the flexibility needed to sit comfortably developed.
Initially the weight of the MK9 caused a noticeable sag where it hooked over my belt. Easily solved with a good belt.
I also found that a real pager has a considerably stronger clip than the dummy pager that comes with the holster. Using the real pager has made the whole rig far more practical as well as stronger.
The draw is awkward and slow by a lot of standards. The solution here is practice, practice, practice. You can develop a reasonable time. Still, since it is a two-handed operation from a deep-cover position, it will never equal a single-hand draw from an open holster. Personally, I would much rather have a 9mm that it takes a second longer to draw than no gun, or a smaller caliber pocket gun which would, in many cases, also take longer to draw.