"P" Valves

[DRE]

The reason some people go with a balanced as well is that it has a one way check valve in it, so fluids will only go overboard. They are afraid of possible infections up the urinary tract from contaminated water entering the tube of the non-balanced kind. The downside with the balanced kind is that urine stays in the tube, so after each dive you have to make sure you clean out the tube. With the non-balanced kind all liquids drain out right after the dive, so I find it less maintenance.
One other reason why people use the balanced kind is that offers one more safety feature: if you loose the bolt and the condom catheter comes undone water still cannot enter the suit because of the one way check valve. I personally started carrying an extra bolt in my flat pocket and the chances of the condom coming off are so slim I'm not worried about that.
Personally I use the non-balanced kind, homemade off of .

Let me know if you have any more questions.
David