Hi, I was wondering, how does this work, if I buy a 1 year or 2 year, is it only a sub? does it expire after that period..or can I still use the product after that period and just not get updates? or does it expire all together. Thanks.

It's a subscription, after it expires you're locked out of your version and can only revert back to Apprentice if you don't want to pay anymore.

Having said that, and assuming that in 2 years the price doesn't fluctuate much higher than in that range (maybe around $350/year $600 for 2 years?), there is no reason to let the subscription expire. It's still one of the most screaming deals to be had, and in 2 years Houdini will likely be that much more powerful (i.e. GPU rendering, forest generators, faster multi-threaded performance, and who knows what else?). Compared to most other options except for Blender, Houdini Indie is by a long shot the least expensive option for freelancers and filmmakers who run a sub-$100k/year operation.

But yeah, it's a yearly subscription.