I'v always worn Arai dirt helmets and Shoei street helmets. After reading some good reviews (and finding a great deal) I decided to try a M2R Rev-X team helmet. It is far better than a cheep thermoplastic HJC that came with a bike I bought but not quite as nice as my Arai.
The good:
The weight and shell construction is similar (To my Arai VX-Pro), the liner is removeable, venting seems ok.
The bad: The liner is not as cushy or comfortable as the Arai, though certainly acceptable. The graphics are a little goofy looking IMHO, the stripes on the visor don't even come close to lineing up with thoes on the helmet. The visor mounting screws are knurled and don't have a slot which led to to think it woudl be a tool free afair to adjust the visor height. This is not so, it is impossible to get the scews tight enough to keep the visor from flopping around by hand, so I used some pliers on the knurled screw. I intend to cut a slot in the screw so as to be able to use a screw driver to tighten it.
Overall, its an ok helmet at a fantastic price. For the price range there is no competition, if money is no concern I would recomend the Arai VX-Pro.
Sorry, I have not tried the Thor helmet.
good luck
btw, I got the m2r at bob's for 69.99:) - msrp is $200 (which I think is a very good price for this nice helmet - my arai was more than twice that).