I have been thinking about getting a Proclip. I have not yet as I am searching for other options before I decide to engage in pulling apart my dash or any other paneling.
So far this is what I have found:
1) No one makes a mount that securely holds a cell phone (or at least an iPhone) that has a protective case (such as Otterbox). There are a few mounts that "adjust" but, imo, aren't that great.
2) Vent mounts are good, but yes basically makes the vent you attach it to useless (although it does keep your phone cool).
3) Side mounts like the one you linked will be knocked by someone who isn't paying attention, and that is surely to be the case should you have a passenger.
4) I absolutely hate window mounts...regardless of what they are for. But, that is just my opinion.
Now, that has left me with (so far) 4 other options.
a) Cup-holder mounts
b) Suction/Pad "dash" mounts
and
c) Visor mount (interesting)
d) 12v Lighter mount (this is what I currently have - it's a Griffin TuneFlex (available w/ or w/out FM transmitter) - though I do not use the aux cable...just BT)
I will take a picture and get it uploaded to show you what the lighter mount looks like. So far, I like it the best...though the way I have it, I have to rotate it to put my key in/out of the ignition (realy not as bad as that may sound)...like I said, I'll get a pic uploaded. It has a bracket (which you can see in the pic) that you slide on which assists in holding the phone securely...but again, doesn't really fit with my Otterbox (it makes do though).