For what they are, they do work well. They do result in a slightly directional pattern to the antenna, and can cause some difficulty in getting a good match. If it's working for you and it's what you want, then it is perfect, and don't let anyone tell you otherwise. I understand the aversion to drilling a hole in the roof of a perfectly good truck. It does result in better performance, but unless you are willing to do the deed, it's a moot point.
I might be looking at it wrong, but I'm concerned slightly about the mount. The outer ring should be sitting down a bit further, more even with the mount. Those "L" brackets are not that thick to create the offset I'm seeing. I could be totally wrong, but it might be worth checking. There should only be the single O-ring under the mount, between the NMO and the L-bracket. While it may not be an issue, on some antennas the center contact won't make a good connection. If it's working correctly, then you are likely OK. What you can do is try moving the whip up and down while it's on the mount. There shouldn't be much vertical play. If you are able to push it down and pull it up with little effort, you may need to take a look at the way the NMO is mounted. Like I said, it could be just the way I'm looking at it, but on a fire engine roof we found someone installed a standard mount on the thick roof. The antenna wasn't making contact with the center of the NMO and causing all sorts of issues. The offset between the center and outer ring looked pretty much like this when I pulled the antenna off.
