I would disagree it's for compatibility testing. More like design rendering.
I have used those quite much, and even if it says it supports flash it won't sometimes display it, it will crash or whatever.
Anyway, nowadays web developers tend not to care and code their pages carelessly, making page messed up in other browsers.
Ever seen the line: "This website is best viewed on Internet explorer" or even better "This website works only in Internet Explorer" ?
Seriously? Wtf? Stick to the standards.