I was very skeptical about it when it just came out because I didn't think that headphone compensation is a worthwhile idea but it turned out to be a very useful plugin.
As sextonr3 I also have a pair of Beyerdynamic DT990s and Sennheiser HD280Pros, but I don't have studio monitors and I use HD280Pros at work and DT990s at home. They sound wildly different, and I figured that even though I know both pairs very well mixing the same material using both tend to mess up my mixing decisions, so making both pairs to sounds roughly the same started to look like a noble goal.
Luckily Morphit does just that and it works very well for the headphones I have. It's been in my monitoring fx chain for a month now and it's not going anywhere, it's just too convenient after you get used to the compensated sound. Mind you, it won't make your headphones "perfectly flat", but it doesn't need to, because there's no such thing as "perfectly flat" anyway. So if you're stuck mixing on headphones like me, give it a try.
I am using the purchased USB Audio Player PRO program with the purchased Tonebooster Morphit Mobile plugin. Plugin is great, but the lacks support for very popular FiiO headphones. Specifically, I mean the FiiO FH7 model. Many of my friends also have headphones from this company and would like the Morphit Mobile plugin to support these headphones. I would be very grateful if you introduced support for these headphones. I hope this feature will be added soon.