I have the Yakima Holdup plus 2 that can carry 4 bikes. We use it to travel to races and also with our kids' bikes. The nice thing about this hitch is that it supports almost any type of bike and almost any size. It won't do recumbents, though.
The hitch with two bikes (the plus two part bolts on and off) is very sturdy and I highly recommend it. The plus 2 extends out from the truck quite a bit. I have it on right now as we are on vacation and am always a little surprised just how far back this thing goes. Even with four bikes, there is very little bounce.
I have only used it hitched to our truck; not the trailer so I can't address that through experience.
Whether two or four bikes, though, the rack has carried our bikes many thousands of miles over the last 4 years. The hitch bolt screws in providing a secure attachment to the receiver and helping to minimize bounce.
You can attached a lock to the bolt. This protects the hitch from walking away although the bike rack is HEAVY so I don't really worry about it. There is also a long cable lock you can buy to secure the bikes to the rack to keep the bikes from walking away.
Speaking about the weight. One person can attach the 2 bike rack but two are really needed if you add the plus 2 attachment. Its both weighty and very bulky set up for 4 bikes.
I check and tighten all the all bolts before every trip and I recommend you add two battery powered red LED lights for viability.