The Mesa Boogie 50 / 50 power amp has been adored since the late 80's. I am not surprised why because this thing just rocks! I currently run my 50 /50 in a rack unit (of course) with my Eleven Rack in front of it. My rack includes: Furman PL-Plus Power Conditioner, Eleven Rack and last, the Mesa Boogie. I use the Mesa to power my 4X12 Mesa Boogie Rectifier cabinet. The "ease of use" I gave a 5 because everything is pretty much laid out to the user. Behind the unit, you clearly see the input as well as the outputs. You can choose what outputs to use so that you are using correct impedance with your cabinet. It features 4ohm and 8ohm and has the ability to link cabs. In the front, There is a power switch, standby and the option to choose Hi or Low power settings (more of this on "features"). As far as knobs, you have two volumes and two presence controls. The features of this amp are also amazing. The reason I gave it a 4 is because currently, the 2:90 has some features that are "more modern". If this was the 90's, I'd give it a 5. Reliability - I have taken this monster to many shows. I mean, it's age for one accounts to it's reliability. This amp probably sounds as good now as it did 20 years ago. When I first got it on ebay, I changed the tubes out. Other than that, it's been a power horse. No issues at all. Value - These things go for $400 approx on used gear sites. There are much more expensive power amps out there but this one for the buck, is BY FAR the best. Those who already know what Mesa is capable of making, know this unit is well made. Customer Support - Mesa customer support is amazing. Called them once about a question I had about re-tubing and they walked me right through it. No problems. Expressiveness / Sounds - Also great. I use my Eleven Rack in front of it and it sounds killer. However, one thing to keep in mind is that the Mesa WILL color your tone. It is a slight adjustment say if you were plugging in to the PA system from the Eleven Rack. The Mesa is extremely dynamic and has a superb response with whatever pre-amp you're running before it. Overall - Great product and I would recommend it to anyone. I play MANY genres of music and it has worked every time. My main style is Prog Metal but like I said before, I have been in cover bands and this thing rocks. Guys, please message me any questions and I'd be glad to answer them! Keep it HEAVY!