Max axle weights for your car will be in handbook but will be difficult to check without access to an axle weigher as used by enforcement agencies. What you must do is ensure loaded rack does not exceed max towbar download(aka noseweight)for you car. If your car has the usual around 70kg limit then this should allow for rack + around 3-4 average bikes. So ok on their own but add a caravan or trailer to this & you will be well over limit unless you have a 4x4 that allows much higher noseweight.
I've got a Maxxraxx, it's a good piece of kit. Only downside is needing artificial crossbar to attach ladies and mountain bikes without a proper crossbar.
If I wasn't towing and choosing one again i'd get one of the carriers that to on the towbar but the wheels sit in carriers rather than hang off the crossbar, as in the bottom half of this page!this page!
I have a maxxraxx and a thule I bought the maxxraxx for when I tow but unfortunately when towing you do not have the 3 feet arc between the folding camper and the bikes I have the one that carries 4 bikes but have only used it with 2 bikes if I was not going to tow I would use the thule as the bikes do seem more secure standing on a platform and also I bought mine with locking clasps which means you can safely leave them on the car I also use a locking cable to lock them together for added security mine is a thule euroway 945 2 bike carrier which in 2009 was £219 pounds, if interested google the thule website they have a number to choose from