I personaly don't think they are worth it at all. But It all comes down to how much labor you want to put it. I bought some 2x4s, a zipper kit, 2 rolls of duct tap, (staples I had on hand, but Ill add them in to the cost as well) and some black plastic sheeting from my local grow store, total cost, 65 bucks, and I have two airtight, light tight tents, 4x4x7 and 3x4x7.
This allows for CHEAP environmental control, as well as cumstomizability. And when I decided to add vents, I didn't care about cutting a big 'ol whole in it because it was so cheap to build, just a little duct, duct tape and time and it was airtight again.
Then again, I have done everything DIY, and I take pride in saying that, but it was out of necessity, the funds are just not present yet.
But, if you want to go spend the dough, you will get an excellent product that will work great.
It comes down to what is worth more to you, your time and effort, or cash.