The Pro Extender, and Euro-Extender are based on the same design. The Euro-Extender has a different head attachment, which is probably still uncomfortable. They are both JES Extenders (most commonly known name for searching).
It is generally a good idea to explore the Review Forum for the various alternatives to any particular product you may be interested in purchasing.
As for alternatives for the JES Extender (also known by many other names, the one I purchased prior to knowing about Thunder’s Place was an andro-penis): The AutoExtender, by monkeybar, is a significantly superior product, in my opinion. He also has a replacement head for the JES which I purchased instead of the full AutoExtender. However, in retrospect, I would have been better off trashing the andro-penis I had previously purchased and buying the full AutoExtender.
You can make your own ADS (see the links in Stevie’s Favorites).
There are also at least two commercial alternatives for ADS that are made by members of Thunder’s Place:
AutoExtender’s AutoADS by monkeybar
PEweights and other things by Monty530
I have used the AutoADS and found it to be both comfortable and effective. I have not used Monty’s PEweights due mostly to a personal choice.
makyen