Although it is designed to carry 4 bikes, i would not feel secure in the sturdiness of this product.
We have carried 2 adult bikes (one ladies but had to purchase a seperate frame adpator to carry this) and one child's bike.
This has allowed us to tow a small wooden trailer across europe, but there is not clearance to have 4 adult bikes and tow with a small trailer.

On the severe downside, we have experienced one of the mounting bolts shear off whilst in transit,

We've just been to Center Parcs using this carrier to carry 2 adult bikes and a small child's bike.

It fits to the mounting plate (which is bolted between the towball and towbar) very easily. The lower end drops into diagonal slots and then you push the carrier vertical and the two top bolts slide into their keyhole shaped mounting points. The top bolts are sprung and have cones on them. As you push the carrier vertical the narrow end of the cones slide through the slots of the keyholes and then the cones seat into holes. This doesn't inspire much confidence when you first do it, but then you tighten the top bolts up using the large plastic knobs (they have metal nuts embedded inside) and you can make the whole thing really solid.

Once the carrier is on the car putting the bikes one is relatively easy, as long as you have enough width between the seat tube and the head tube on each bike. The bars the bikes hang on are ~400mm apart, this was fine with one of the adult bikes but was a tight fit with the other one as it has a mounting bracket for a child seat attached seat tube and that reduced the distance between the seat tube and the head tube. The child's bike fitted with one bar going through the rear triangle.

The bars that the bikes hang on have moulded rubber seats on them, there are 4 sets and you can't remove them due to an end cap on the bar, but you can slide them along the bars and rotate them. The seats have thick rubber straps that go over the bikes frames and hook onto the seat. These are actually quite solid and hold the bikes quite well.

We used additional straps (the carrier comes with one) to hold the bikes really solid and pipe cladding to protect the frames where they touched the carrier or each other, this worked really well. The bikes are held well clear of the rear of the car, there was no chance that the bikes would damage the car and no need to twist handlebars or remove pedals.

To put the carrier on the car and load the 3 bikes took 5-10 minutes.

When driving the carrier bounces a little but that's true of all bike carriers in my experience, the bikes obscure the view from the rear view mirror and so you have to drive using the wing mirrors. They also obscure the number plate and the lights so you need a lighting board (as you need a towbar to fit this carrier to, you should have the socket for the lighting board as well).

Off the car the carrier folds relatively flat and will fit in the boot, or in the passenger side (resting in the footwell and leaning on the seat).

On the negative side.

It's designed so it doesn't obscure the towball and so in theory you can use it and tow at the same time, however the bikes are carried so low that I would not even consider towing while using it. To be fair all the cycle carriers that allow access to the towball while they are fitted (like the Maxxtraxx) make it clear that using them and towing at the same time should only be attempted if you are sure that it will not damage the bikes, the car or the thing being towed. You also have to ensure you don't exceed the nose`weight for the towbar.

It's also designed so you can loosen the mounting bolts and lower the carrier to give access to the boot with bikes still attached. We didn't try this and it looked like it would be quite hard work (and definitely require two people) to raise the back up to the vertical position and get the mounting bolts reseated properly.

The final negative point is that it's designed to hold 4 bikes. but I wouldn't feel happy with 4 adult bikes on the carrier. It just doesn't feel sturdy enough for that.

All-in-all this is a good carrier for the price, easy enough to fit to allow it to be removed as soon as it's not required, small enough to be stored unobtrusively and solid enough to inspire confidence.