This is something I would be very interested in too.
I've got some roofbars for my saloon, and to be honest, they're crap. I originally bought Paddy Hopkirk when I was due to go on holiday in preparation to pick up a kayak on the way. I got to the hire shop and found that the bolts in the Paddy Hopkirk bars were too short. They work by nipping onto the trim around the window, with a bit of rubber trim around the edge to 'protect' the paint.
I had to buy some bars there and then from a motor accessory store next door (no - they didn't sell bolts - gits). The bars I got were almost identical but with a longer bolt, and cost about 25 quid. They were the same design - a little bent bit of metal which bolted to another, nipping the gutter.
The saloon just doesn't seem to take to roofbars very well at all. I'm a kayaker, and have a mixture of things to carry, including an 18ft sea kayak and the problems seem to be the distance achievable between the bars, the bars touching the roof and the fragility of the window trim. If it's just snowboards you're going to strap up there it'll probably be fine, but anything of any weight or length (roofbox, kayak, timber etc) and I wouldn't trust the gutter style bars at all. I'm also extremely wary of bending and creasing the door trim. I get really nervous with things on the roof of my Omega - more so than any other car I've had.
The Mont Blanc ones look to be the 'nip the gutter' design - and I'd be really interested if Vauxhall have something different that is more secure. I can't understand it - the Vectra of the same age has captive nuts in the body to receive bolts and it's extremely sturdy - but the omega saloon has nothing like it (that I've seen).
Are Mont Blanc and Paddy Hopkirk the same? Not sure - perhaps they are the same company...
Let us know what you go for - and if you do get the chance to see some Vauxhall ones what they're like and how they fit!