Spin Class for Summer interval rides??

Besides the bike handling aspect, what are some of the other disadvantages of doing spin classes as my interval rides?? I do my best to set up the bike to mimic my own and I basically stay in aero (also known as "position 3" to all the spinners. LOL) the entire time unless I'm cranking up the resistance. Also, I don't mess around with changing my hand/butt position like the instructor yells out trying to imitate an actual ride as well as possible.

I definitely notice that I work way harder in the class as far as my HR is concerned and my legs are on fire pretty much the whole time. I still try to get at least one shorter ride in a week and I always get in my long rides during the weekends on my actual bike (In the AM)...at this point in my training about 50-70 miles. The only reason why I'm opting for this now is because it's been anywhere between 110-115 this summer with no sign of relief...Mornings are doable, but they still suck!

So is this sufficient??