They're ok - I've got one. The adjusting "buckles" on the straps aren't very secure though, and I always knot mine as well for a bit more peace of mind.
I only ever carry one bike on it though - like most racks of this kind you'd need to do a fair bit of faffing with pipe insulation or something to keep two bikes from ratching against each other.
I've got pipe insulation gaffer taped on mine where the two lower tubes bend inwards to stop crank arms etc. fretting against it.