Least effective for Mustangs or just any vehicle? I've seen good reviews for them on lightnings. Either way I'll have to look into it.
Any vehicles because the design of the can doesn't change no matter what it's used on.
You have to remember that how much oil a can catches is only part of the equation. In my opinion, the most important aspect is how well does the separator keep oil out of the intake.
A lot of people only focus on how much oil they are catching but don't check the outlet line to see if liquid oil is still passing through the can. No can is 100% effective but the best ones will only show trace signs of oil such as a slight film which is what my Bob's can and my newer style four chamber UPR show.
My original style UPR can and the first version of the four chamber UPR can would get liquid oil in the outlet lines which told me that they were not as effective as my other ones.
While I have never personally used a JLT can, I have read many accounts of liquid oil being found in the outlet line, even using the upgraded latest version of their can.
A lot of people like this can because it uses factory connectors and lines and is very easy to install and remove. Some people have experienced the plastic fittings on the can themselves breaking causing a vacuum leak. This can is also not attached to anything other than the lines which some people consider an issue.
There is a lot of information out there on oil separators and the different brands, it just takes time to find and read it all.
2014 GT, Sterling Gray, base model, Automatic
GT500 AB, GT500 OTA pipes
Bob's oil catch can
Ford aluminum finned diff. cover
Ford all weather floor mats
Ford trunk liner and cargo net
Ford locking gas filler plug and wheel locks