They are nice, I like using them. Yeah, those little recesses are great for sorting and keeping parts from rolling around. These silicon mats do have a couple issues to consider: 

* Not anti-static.  I am very conscientious how I handle my assemblies on the mat. The biggest gotchya is when let go of you project on the mat, move around, rub against something else then touch your project again. No-no. You can also charge up your project with your body getting charged by your clothing rubbing on you. Meanwhile, your part is nicely insulated and charging with you. When you move your part to another surface it can discharge to that new surface's potential.  Some mats have a coating that might only last until your first cleaning.

* The high friction surface of silicone is very handy. Keeps your project from moving around, however, that same friction surface makes it hard to clean. You can't brush off dusk and particles as easily. Forget about that old habit of gently brushing clipped leads or anything aside temporarily with you hand, the object will stick to the mat and stab you finger or hand. Been there, done that.  Dust just builds up and seems to stick. The dust also sticks to the underside if you move it. When this happens the mat doesn't "stick" to table as much and can slide around more easily. It takes soap and water to clean it well. 

That said, I still wouldn't want to go without the two I have. Just keep what I said in mind. 

Sounds like it's worth a try, thanks for the heads up.

i mainly use that type of silicone mat for doing hot air rework, it works well for protecting my desk from burns, but i've used it before for doing assembly. for hand placement of SMD parts,  i generally use a hackaday stick-vise to hold the PCB, then use some SMD tape/reel holders to secure the parts. I also use a vacuum pickup tool of my own design for pick-n-place.

https://www.tindie.com/products/FemtoCow/set-of-7-smd-soldering-trays-/

https://www.ebay.com/itm/5-way-SMT-SMD-1206-0402-0603-0805-reel-Feeder-4-DIY-Prototype-Pick-Place-solder/290875427111

https://hackaday.io/project/19189-diy-vacuum-pickup-tool

http://www.stickvise.com/

Thanks!