Comfort:
One of the important things for most is how it feels. In this case, I would say how much it doesn't feel. I'm wearing it right now seated and I can't tell it's on unless I lean back and shift to press the gun against me, but even then there's no pain. The big piece of leather does it's job very well. It may look a bit ungainly, but it really is not. The leather cups your body and is really soft. There's no need for an undergarment to "shield" you from the holster.
Concealment:
Take a look at the pictures to see how well it conceals when tucked. Note that in these pictures my arms are over my head to pull my shirt tight.
The velcro clips work, though sometimes you have to shift them up a little bit so the rounded part of the clip doesn't show under the belt.
Clips:
The Comp-tac clips are thicker and look more study. Instead of an adhesive/glue to keep the velcro on they wrap it around the clip and staple it twice. I haven't noticed the velcro peeling/moving at all. Comp-tac designs their clips with a total of three holes to aid in adjustability. Their clips are cut square at the top end which maximize the amount of velcro that hits the belt. They are also very well finished so there are no sharp edges or ends.
The Crossbreed clips are thinner and since the velcro is glued on there may be a chance for it to peel or move some. I haven't observed any peeling/movement yet. They only have one hole located at the bottom of the clip. Crossbreed relies on the multiple holes on the holster itself for adjustment. This works well because it doesn't reduce the amount of shirt you can tuck in behind the clip. The clips aren't well finished as the sides aren't rounded like Comp-tac's. The tops and bottoms are circular so they don't have any corners you have to worry about.
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Mine
Sig P239 (9mm)
Norinco 213 (9mm)
Kel-tec P-3AT (380)
Bersa Thunder22 (22lr)
Wife's
Ruger SP101 3" (357mag)
Walther P22 (22lr)
Charter Arms Undercover (38spl)