it wont necessarily be bad for the engine, however most ebay intakes are very low quality build-wise. i have bought an ebay intake, once, and i will never again. it was held together with some cheap glue, and with the high engine heat, the filter end came off due to the glue melting. do yourself a favor and buy a K&N brand filter. They are high quality, and you can clean them every so often so they last for a long time.
The old saying goes " you get what you pay for ". I have heard of a few people buying these cheap intakes...only to find out that the cheap air filters that come with the kits have been known to separate and cause dirt to get inside the engine. In this case I would spend the extra coin and go with a well known reputable brand.