Hi Todd, thank you for a very valid question.
There are no other BBA approved products on the market that satisfy fully the British Standard for loft ventilation and because of this the cheaper versions may well help ventilate the roof, but they can also create other problems. For example, Lapvent has a mesh guard which prevents all types of infestation, it also has a self closing pressure valve, which eliminates any risk of storm force winds driving through the roof and lifting tiles. It also has its own storm baffles which will prevent any water, snow or sleet being driven into the loft. Check out the alternatives and hopefully you will identify these differences. Im sure most people would appreciate not having to deal with a wasp nest due to an unguarded opning in the felt. I hope this helps.