I am a Denver Massage Therapist for 25+ years. This is a very good product. It should only be used by those who have had and enjoyed deep tissue massage before. The blue ones are softer and more appropriate for the general public. There are videos on youtube with usage instructions for this specific product and for smooth foam rollers. The exercises for both are mostly interchangeable.
I use mine for front back and sides of the upper legs where it is much superior to the smooth foam rollers. I also use it for my neck by laying it under my neck while on my back. I turn my head left & right as far as possible and get a nice massage there. I also lay face down with head turned to the side and move back and forth to massage front of the neck on this device. Be careful in this position though, if you get light headed then back off the pressure as you may be restricting blood flow to the brain.
I personally do not use this much on my back though for many it can be great. For my back I use very hard rubber balls like La Crosse Balls or the hard rubber dog balls you find in Petsmart. Those are the core of my self massage for trigger points on back, upper arms, sometimes the outside of the upper legs (aka abductors, facia Lata etc) The balls are also good for sitting on for the glutes. The rumble roller is good for this too I just like the deeper more pointed pressure of the hard balls.
A final product I am looking at but have not yet bought is the Super Nova massage ball about the size of a cantaloupe which, like rumble roller, also has hard knobs but these are flat topped. Take a look at that as part of your self massage tool kit.
Good luck. Let me know if you find any other interesting deep tissue products.
The RumbleRoller models, clockwise from left: will appear with these firmness types for the : RRX317 RumbleRoller, extra firm (black, 36% firmer), RR316 RumbleRoller (blue, original density less firm ), RRCX127, Compact RumbleRoller, extra firm (black, 36% firmer), RRC126 Compact RumbleRoller (blue, original density) Please see which level is the best for you.