Like all Apple stuff, you pay a ltitle bit of a premium on adapters like this, but they always work the way the're supposed to. I'd say $20 would be a more fair price for the TB to DVI adapter, as functionally equivalent examples can be had for that price (or better) online etc,
My only "complaint" with this adapter would be that the cable is super short (just a few inches) meaning, if you're using it on an iMac, then your DVI cable will be pulling down on the adapter and wearing out the port. I returned mine and bought an adapter off of Amazon that has a long TB cable (like 6-10 ft.) so the heavy connector is at my monitor.