After a little over two months of doing these, I thought I would summarize the advantages I have found for doing these jelqs vs regular ones. I will be calling the corpus spongiosum "sponge", and the corpus cavernosum "caves".

1) People with weak grips or small fingers will find these will help with the jelqing.
2) Much stronger grip using this two finger ok grip vs regular grip.
3) Two fingers riding up your sponge is very much more effective this way. In fact, JP's beginner program calls for three sets of 50 regulars and 30 v's. UJ's are so effective that I have reversed that, doing 50 v's and 33 UJ's per set because my sponge is gaining incredibly and I didn't want it getting too far ahead of my caves. The reason I am doing 250 jelqs is that basically I am looking at maintaining with slow growth. I was doing more than 500 per set before, but decided to cut back.
4) At the completion of your first UJ you keep your hold around the base of your glans as you grab your unit with your other hand to begin your second UJ. When you get your regular grip your shaft expands, but when you then add your middle finger it expands amazingly more. There is a ton of material about to be jelqed up your shaft, and you have two fingers working at seeing to it that none of it escapes as you proceed.
5) While #4 above is great for girth improvement, additionally, your veins will be pumped up to the max. Personally I like a shaft that shows a lot of large, strong veins, and UJ's are just what the doctor ordered for me in order to get just that look. Bigger, stronger veins equates to more blood flow within your shaft, which promotes a more healthy unit. Health is good, but it looks good also. I throw in strong kegels just before I grab my unit to add even more expansion.
6) By being more effective moving blood up your shaft, you are also expanding your glans better than doing just regular jelqs.
7) Since UJ's are more intense you can get the same or better results from doing fewer of these than regulars, thus saving time.

Some personal stuff that I do and like is that I always jelq downwards, and while performing UJ's I really like how my unit looks. As I jelq downwards toward my glans, the ribs on my shaft are very pronounced, and my veins are also. I absolutely love doing these bad boys. I am pulling my unit rather strongly while doing these (I use a ton of lube to make sure I glide smoothly), so it should help some with length. I like how it feels, I like how I look, and I look forward to doing them. I always enjoyed doing v's, but UJ's top them by a mile. Doing these is not work, it is pleasure - so setting time to do them is easy.