Who has used these on a swim jig ? What size would you recommend for this application? I've never seen them in person so I'm unsure of the true size... I know what they say the sizes are but we all know that varies by company

i've used the 4.5 on a chatterbait as a trailer. has nice action and they're relatively cheap. 

I've also used the 4.5 with success, on a 3/8oz swimjig. They've got more body roll than a lot of swim trailers because of the back-facing ribs on them. And as @EWREX said, YUM is cheaper than others. Summer gill was the color I had success with.

This might help

 

From left to right Zoom super fluke 5.25, Yum 4.5 pulse, Yum 3.5 pulse, Keitech 3.8. IMO the Yum 4.5 is thick, I know its ribbed, but its still fat. A 5/0 hook I think. The 3.5 size is a nice drop shot bait. They both have a very shallow slot on top. 

Thanks for the responses looks like I'll get a pack of the bigger size in summer gill

 

They're a great bait. I like the smaller size on a jighead and the bigger size as a trailer.

Last year on vacation I picked up a couple of packs of the 3.5 size on a whim while picking up tackle for my buddy watching our house. 
 

They worked great on a couple different brands of 1/4 ounce swim jigs. Not sure if I would even try the bigger one, maybe on my 7/16 jigs? To me the profile just seemed right with the smaller size.