Was at the local art supply store (Curry's) earlier and discovered they carried Uni-Ball Signo white gel pens. I've ordered them previously from Jetpens after hearing how great they were and was not disappointed in the least, so I had to grab a couple. The text and design is slightly different on the ones I grabbed locally -- no Japanese characters, the body on the Japanese model is all clear, the English one is frosted white.
I decided to test them to see if they were any differences other than the language. As I started to set up the test, I realised I could share the results, so I added the Sharpie Poster-Paint white marker into the mix. I also use Pilikan Graphic White with a brush in the studio as well as the Pentel Correction Pen, but both are so different in use or application than these tools that I left them out.
I set up a variety of inks, leaving out both India and acrylic inks, which are also studio tools -- I generally use these sort of pens at cons, so thought it best to try them on the inks I'd also be using in that situation.
Overall, I'd say it looks like the Japanese and English pens are identical. The Signo pens have a slight edge on the Sharpie as it seems to absorb into the Copic and G-Tec slightly more. All three do well on water-based and waterproof inks.
Hope this useful!