Has anyone used a Mont Blanc inverter roof carrier, the one that holds your bars and saddle rather than your wheels/downtube?

Are there any problems with having the bike upside down for a long time (thinking forks and disc brakes).

I'm tempted by a cheap roof carrier (already have the roof bars), and have seen this one Mont Blanc CM25

I'm always a little worried about the downtube clamp carriers and spend the whole drive looking out the window to check the bike is still on!

The other one i've seen clamps all the way round the downtube. Probably a pain to get the bike on it, but no chance of the downtube coming out of the clamp, even if it comes loose Bici

Any other cheap ones i've missed?

If you have an estate with roof rails and can position the roof bars to match the wheelbase of your bike then you can buy these and bolt them to your roof rails. Low profile when the bikes are off and lockable. I've fitted three to my bars. It's a 5 minute job to take the bars on and off and there's no additional faff with the bike carrier. The rear wheels are strapped to the bars. The only problem is you have to put the from wheels somewhere.