They definitely can work, but they are not a magical suit. They are just one piece of the puzzle, and unless you are "all in" on scent control, don't waste your time. The ones who say they don't work at all, have never been "all in". The hood and breath shields are the most important parts of the system, and most that have only used the jacket and pants say they don't work. DUH, NO KIDDING!
I have a complete system of scent control that I have been perfecting over the last 15 or 16 years, and ScentLok plays a big part in my system. I usually let countless does and 25-30 different bucks walk by at spitting distance every year, several are directly down wind. Most are 1-1/2 year old bucks, with around five or six 2-1/2 year olds and a couple 3-1/2 year olds. The 3-1/2 year olds are my target bucks, since it don't get any better than that around these parts. This is in heavily hunted Mid-Michigan farm land, woodlots with seas of corn and beans. Educated deer, that have a PHD in busting people.
I do not hunt the early HOT season. Our season started Oct 1st, but I probably will not hunt before the 20th for the first time. If it stays hot, I may not hunt until Halloween. I honestly cannot remember the last time I was winded by ANY deer while hunting. It's been 8-10 YEARS, at least! That was while I was still perfecting my system. Either you are "all in", or you can whine with all the ones that "KNOW" it don't work. "ALL IN" aint easy, but I don't even worry about the wind. Seriously! I just hunt, and see lots of deer within bow range, that have no idea I'm even in the woods with them.
As far as garments go, I have used the ScentLok and ScentBlocker/Scent Shield brands. The one ScentBlocker pant and jacket were not very well sewn, and were not very durable in the field. This was the first year they came out with them (around '99 IIRC), so they may be put together better today? They did cover the items under warranty, and replaced the whole outfit with the help of a good dealer. The dealer exchanged the ScentBlocker for ScentLok, and I never looked back. Used ScentLok before and after the ScentBlocker. ScentLok brand have always been very comfortable and durable.
Not magical suits, but one of the most important pieces of my scent control puzzle while hunting. I cannot do what I do without them, I've tried and failed, several times. But it wouldn't work without all the other "ALL IN" scent control measures I take either. It's a system!