I have used several models at urinals. The TSW diamondback and eroticreations both worked well, but require one hand down your pants holding the receptacle in place while you pee, and the other hand guiding the shaft.
The best one I've used to date, that I can just whip out of a fly and go (without even holding)is the new emisil one. They haven't released it yet, I'm currently just testing it for them, but it should be out soon and I HIGHLY recommend it.
With any STP, wear underwear with a fly hole. It helps to get the correct angle of the shaft for gravity to work in your favour, also hides the harness you may be wearing.
As far as tips, I just walk up, unzip, whip it out, and go. Even when I had to use an extra hand down my pants no one really noticed. Stand close to the urinal and no one can see what you're doing anyways. Make sure you get your shaft pointed at a good angle for your receptacle to drain, and make sure you're holding it far enough back. You'd be surprised how far back your pee hole is, most guys don't actually know or hold their STP right.