Got the Seidio Active Combo today.
The case itself is good, but as a combo (with holster) it is terrible. It definitely has a huge flaw in design (not only HTC 1S case, but others too). The holster clip part that supposed to secure phone to the holster pushes back the rubber and most of the time does not engage. If you put the phone in the holster without looking, and let it go thinking that it is secure, phone just falls back most of the time. I would say that it would cause more damage to the phone using this combo case rather than just a naked phone.
Another thing I just can't understand is why they left such a huge gap in between the case and the holster. Screen doesn't touch the holster anyway due to the silicone lip around, so they just made the combo about 3mm thicker than it needs to be. Again, bad design.
One thing I like about the holster is the belt clip. It feels much better than otterbox cases that I have tried before (not with this phone though).
Case only - good.
Combo (case/holster) - terrible.
Also quite overpriced for what it is.
The only way I could make it useable is by cutting off the top rubber piece, which made it a lot less attractive. Alternative would be using glue to attach rubber piece to the top of the phone so it can't be pushed back, but that means potentially messing up $500 phone with glue residue.
Seidio really needs to fix this huge design flaw, because it is the same issue not only with this combo, but also with their similar active case combos for other phones.