I purchased my Tundra only a few weeks ago. It came with a drop-in liner. While pressure washing my truck I was curious. I removed the drop-in and found that it had completely messed up the paint. Not to mention the previous onwer(s) had drilled multiple holes in the bed.
I welded the holes solid and painted the exposed metal on the underside. I paid $440.00 for a spray-in liner and I must say I'm impressed. They removed the access panel to the tailgate, all tie-downs before application. They did an excellent job.
Pros: Cargo (groceries in my wife's case) does not slip. Most imperfections in your bed will be covered. (This stuff can be applied almost as thick as you want it.) You can pressure wash it (3600 psi) without concern. It looks GREAT!
Cons: Cargo does not slip. (I guess you can't get the both of both worlds.) When loading a large heavy piece of hardware (a door in my case) you can't exactly "slide" it into the truck.
As far as "bed mats;" I've never spent the money. In my first truck I purchased an old blue gymnastics’ mat from a local gym. Can't remember the price but it was CHEAP.
Pros: Crease in the middle of the mat mad it easy to fold and install/remove. If necessary you could move it to one side. It was covered in blue rip-resistant nylon "stuff". I hauled a lot of stuff and it never ripped and it was easy to wash. I had a camper that I would remove for months at a time and it never showed any significant signs of sun damage.
Cons: I had to cut it to fit around the wheel wells. After many attempts to cut it I found that an electric meat knife works perfect. I also drilled two cup (beer) holders near the tailgate with my dewalt. Unfortunately the blue "stuff" was fairly slick and cargo would move,
In my next truck I purchased a piece of 3" fire retardant foam.
Pros: MUCH more comfortable than the gym mat on camping trips. Cargo/groceries didn't move. After applying a meat knife the foam it fit absolutely perfect in the back of my truck.
Cons: Stuff/cargo didn't move. I eventually added a Yakima rocket box where I could stow the foam when I needed to move something "big" or awkward. It didn't have a washable cover. If the gas can spilled over during transit my truck would stink for a month.
Be careful purchasing foam! Most places will try to take your head off. Go to an upholstery supply store and you will save at least 50 percent. I paid $40.00 for my piece of foam.
I've searched and searched and I cannot find another gym mat. But I must say it has been the most functional, least expensive, and best "bed mat" I've ever used.
It's not for everybody, but I'm hoping my experience will help a few.