Hi jimmy, change stock air filter to open pod filter will increase HP, that is true, but you can feel it only at HI REV, b'cause the open pod filter can allow air suck in more faster then the original one. Ofcourse open pod air filter have the week point too.
Engineer use alot of time to design the air intake system for street use, so the air filter must have excellent filter function, and also most of the car today got air box design, why? to make a car easy to pick up at low range rpm or increase the torque at low rpm range, the air flow in to the engine must be fast, so engineer design the air box to store the air inside, allow engine more easy to suck the air.
But at HI REV rpm, engine need huge amount of air, original air filter have excellent of filter function but at the same time it limit the amount of air to go trough. So race car don't have the air filter, b'cause they stay at HI REV rpm range all the time, they don't care about low range rpm pick up or low range torque.
So remember, low range rpm need the speed of air flow, hi rev rpm range need the amount of air. If you don't believe, try a very easy expirement, take out the air filter together with the air filter cover, then try a few run, you can feel the engine is more easy to rev to high rpm, but at the same time you can feel your car is less power at low rpm range, specially when traffic jam.
To you jimmy, just base on your driving style. ^_^