Roll Bars (again!)

[strat]

I would first like to apologise if I am asking stuff that has already been asked... After having seen pictures of rolled Tivs, I am seriously considering buying a roll cage. However, since the manufacturers say that they've not been been certified or tested, I am wondering if they are purely cosmetic, or if they might offer some genuine protection in the result of a roll? Also, there are one or two different ones on the market...Are they basically the same, or is there any discernible difference (except price!)? Any information would be greatly appreicated.