Well, to answer your first question on side effects...you may feel more aggressive and a stronger libido from Xenabol. With Clenbutrx you could feel shakey or headachy for a few days until your body adjusts. None of this is major.
AS far as keeping your muscle hardness after using this stuff, well, that will depend on your diet. If you keep eating well and training right you will keep alot of what you gain, but not all. You may take 2 steps foward and one step back.
I would use these products to help with a plateau or to reach a "peak" condition, and then go back to my normal regimen.
In a way its like guys that use steroids...they may gain 25 lbs while on, but will then lose 10-15 after they come off. If they are really smart and dilligent about their training and diet once off they will keep more than the guy that stops training hard and eating well...but there is no way to keep ALL of your gains.