I think the whole point of a USB ASIC miner is to take the hard work away from the GPU (or CPU).

Unless there's a way of running separate mining jobs on both GPU and ASIC, I don't think a USB miner will damage your laptop at all, as the GPU won't even be used.

Whether a USB miner does a better job than a GPU for mining I don't know. It's certainly more customised for mining than a GPU is, and I'd imagine far more efficient.

But I don't have enough experience on this and welcome any corrections. Perhaps a GPU is still better in terms of raw hash rate.