Prior to my friend getting a LQ trailer, I camped with a truck tent for about 5 years. It works well as a poor-man’s living quarters! 
A couple of my friends had them too. Any time we’d camp we’d have people stop by and want to look at them.
I had a “Truck Tent” brand that I don’t think is made anymore. The Kodiak looks to be the most similar style–sort of shaped like a Conestoga wagon rather than a tent shape, and it has an integrated awning/cover over the opening. My friend had a Sportz brand with an awning. I’d highly recommend something that has some sort of extended awning/cover over the opening.
There are a few different designs–one with an attached bottom liner that covers the truck bed and one that just attaches to the rails with no liner.
I had one with no liner, my friends had a liner.
With an attached liner you need to completely unload the bed of the truck prior to setting it up. With the kind I had, you could leave cargo in the bed and the tent just went over the top of it.
The pro of the attached liner is that the condition of your truck bed doesn’t matter as much, and it can help keep your stuff cleaner.
Because I didn’t have an attached liner, I wound up getting a Bedrug brand bed liner that stayed in my truck. It was very cushy and made it possible to crawl/kneel in the bed with no problem. The only downside is that if you want to haul dirt or hay it can be a PITA to clean off.
Another thing to consider is the compatibility of any sort of bed cover with the tent. I had a truck with a roll up style bed cover with rails and one with a completely removable bed cover that clamped on with no rails. While I could use the tent with the roll up style, it never fit as well as with the kind that just clamped on that I could completely remove.
As you said, probably the biggest disadvantage of a truck tent is needing to remove it if you have to use your vehicle. It wasn’t a big deal for a weekend camping trip, but when we’d go on longer trips we’d usually have to do a supply run.
The biggest piece of advice is to set it up a couple of times in your driveway before you go camping! The first time I used it, I wound up getting delayed on the road and got into camp much later than I had expected. I had to set up just as it was getting dark, and because I had practiced it wasn’t a problem at all.
