Recently got myself a long (or large) version of this strap. My main reason for buying this to use it with Schecter Hellraiser Hybrid PT-7 electric guitar, which is really heavy and demanding on your shoulders with a standard strap. So, yes! This can be used with guitars too!
L size would mostly fit anyone but if you are really big or really small, you also have s and xl options. The best thing to determine the ideal length is to measure it with your current, regular strap. Just adjust it to the right length and measure it.
I almost don't feel any weight of the guitar anymore! It locks in a nice playing position and feels safe and secure all the time.
The only drawback, in my opinion, is that it's a bit overpriced, I would like it better for 50€ :)
Also, these straps feature double holes on both ends. Unless your guitar features double strap buttons, it's almost impossible to fold the end and use it on a single strap.
On the right strap button, I use the hole on the wider section, but for the let strap button, I go with the second hole. Otherwise, this part sticks out and you may feel it when you play above the 15th fret. Not a big deal though! At the end of the day, these are built for bass guitars.
I definitely recommend these to anyone using heavy instruments such as LP type of designed guitar with mahogany body (usually this is adding too much weight). Hope this helps, cheers
Osman