I tried it. I put my (full face)shoei on and went for a quick fly about. Hopeless. no attenuation of low frequency noise at all and totally horrid in a hot cockpit with the visor down. Was only up for about 3 minutes and that was too long. My Alpha is built for the job. No comparison, not even close, and it just felt wrong. Maybe an open face would feel better but I wouldnt even consider it. If you can afford to get a PPL and you want a helmet at all, get a proper one. The pain of the cost soon fades. I cant even remember how much mine cost.
I've said it before on this thread but its worth saying again. The Alpha tinted visor alone is enough reason to wear one.