I've now replaced my regular (daily / near-daily) masturbation habit with using my Fleshjack in order to check it out thoroughly.
The main thing I've noticed is you should be fully erect when using a Fleshjack. Having a soft or semi-hard dick prevents you from experiencing the full pressure of the Fleshjack sleeve. While it's still possible to get some use of it at that point, you may be better off using your hand at that point; your hand permits you to regulate the pressure necessary to get yourself off while the Fleshjack's (original sensation's) pressure is uniform throughout the sleeve.
The experience between using it while fully erect and soft is dramatically different. When I've been erect, the experience leaves me short of breath, panting, and with a hastened pulse that lasts for many minutes. When I've been soft, the experience leaves me with the sense of an average / adequate masturbation session.
One thing that's nice about the Fleshjack is when you shoot inside of it. As long as you take it off parallel to the floor, your cum will stay inside of it. This eliminates the need to dry off yourself (if you prefer drying off your cum instead of keeping it on yourself). Instead, you just rinse out the sleeve and the case and let it dry.
You should probably not use your Fleshjack as for long-term cum-storage if you're into that. (Samuel Colt, http://twitter.com/SamuelColtXXX, warns against keeping it there because the cum [apparently] starts to ferment).