I use pedal extenders on a lot of my bikes - the ones with flat pedals where I am not cleated in.
You don't want to use that particular brand or its many clones. They have poorly cut threads that fit loose in the crankarms, and rely on being forced down tight to push against the crankarm to stay stable.
These Sunlite ones are of good quality, but not stainless so if you live on the coast you'll get a little rust. The ones I have on bikes away from the coast never rust.
This set worked quite well for me. Note the 16mm length, not the standard 20mm. Usually when a seller claims an extender is less than 20mm they are mislabeling it. These really are 16mm and you will probably be well-served by using something as narrow as you can get away with. Increased Quack Factor is not always good for people (It is for me, I've found)
I have a few sets of USA-made ones that were made by a machine shop that sold on EBay, but I can't find them online anymore.