#3
While that does say "Rack Mount Amp Case" it does not appear to actually have anything in particular for amp usage (it sort of looks as though there is some sort of thin padding on the inside, but it doesn't say in the text, so...).

This might be too obvious, but do remember that a lot of amp heads are too wide to fit in a normal 19 inch rack. The 6U tells you how high it is, 1U 1.75 inch. Most rack tuners are 1U.

Make sure that there is enough room for both your amp, and something to keep it from bouncing around in there.

If you're only looking for a hard case to protect your amp, I would suggest one which is specifically made for this, rather than a rack case.