The U's are in the offensive backfield

[Zebra29]

When using this mechanic, the U can help, but the L might be most valuable in his position, holding the line of scrimmage. He should have a good angle on most of these. The exception being when the receiver is going away from him.

[Bob M.]

REPLY: Regarding the catch/trap of low passes...I did ask an NFL friend of mine who said that they don't yet have a prescribed means of compensating for this deficiency. He also did remind me that this is only an experiment for weeks 1 and 3 of the pre-season.

[With_Two_Flakes]

This would be my major concern especially on the smaller size crews.

I worked the wing on a 4-man crew here in the UK a couple of days ago and was screened out on a reception. I had no clue whether the kid caught it or not (usually you have a gut feeling one way or another). Luckily I had a decent Ump on the day and when I looked across for help, I got eye contact and the slight affirmative nod.

[Forksref]

I agree that it probably won't filter down to the 5-man mechanic. The L and LJ are downfield on passes and with the U in the backfield, we'd miss ineligibles and the help on coverage of the hook passes to the inside. I don't see the advantages, even in the pros. I've noticed some pretty intense sprinting to spot the ball, too. Normally, the U is near the end of the run and can easily get to the spot. The 4 NFL guys at the clinic we were at in June were not endorsing it and I suspect that they weren't as vocal as they'd like to be about it. Maybe feedback from the preseason experiment will change their minds.

[l3will]

Here in Minnesota, the umpire is already placed in K's backfield for
punts. He is responsible for the snapper, interior numbering exceptions
and line play.

Most umpires here like it...

I'm not sold on it, since it makes for some interesting decisions when
K decides to be A and go for it... does the umpire sprint back behind
to his normal position? I'm sure you can think of many more dilemmas for
where the Umpire should be positioned.