You'll be fine using the wide gate, i did so myself at Leicester at the weekend, i did not hear any tutting behind me.
I'd honestly be shocked if someone
did say something when someone who appears able-bodied uses a wide-aisle gate. It isn't only for disabled people, and in my experience it is very helpful when people spread themselves out across all gates, including the wide-aisle one(s). The only issue I have is when people start tailgating while using wide-aisle gates, and it is extremely common. In the situations where I have been operating a gateline (station control unit is directly next to the wide-aisle gate in this case) at a busy time and someone has had a ticket rejection, they go to the wide-aisle gate to get let through manually. The problem with this is that others will stand too close behind and either walk through without presenting/using a ticket, or everyone will start showing their tickets to me rather than using the barrier properly. I'd be happy to manually check tickets as it's a bit more fun, but I need to be able to look around for people entering the other side with bikes/buggies/wheelchairs, and I need to be paying attention to any problems with the standard gates. Another issue with the wide-aisle gate usage is that everyone is afraid to use it until one person does, and 90% of the time it's someone with a rejected ticket and it causes the exact problem I mentioned above.
Beyond this, people stand too close to the gate when presenting a ticket so it won't open, and they have little space to step back as people are too close to them. The worst situation is when people are attempting to use one bi-directional wide-aisle gate to enter and exit simultaneously (with large objects so they can't use the standard gates), or when a cyclist enters against the flow of people (2 trains worth of people leaving, 1 cyclist entering). The cyclist certainly gets priority as they actually
need to use the gate, but no matter how much you tell the people exiting to stand back and wait, they will always try to walk through when the cyclist tries to enter.
My summary for etiquette would be:
Use a standard gate if there aren't queues, they're just slightly quicker.
Use a wide-aisle gate if you are travelling with anything heavy/large. If the gate is free, take children through it as well as it is easier and safer.
Allow anyone who
needs to use the wide-aisle gate to go through first. This includes cyclists, people with reduced mobility (wheelchairs, walkers, etc), buggies, and heavy luggage.
Stand
off of the barrier's metal platform until the gate is actually open, and keep any items off of it as it might not open otherwise.
Tap your card/scan your ticket/insert your ticket unless any member of staff is directing you through - I have seen gateline staff keep the gate open and manually check tickets to keep things flowing more quickly. You still need to tap your card if using contactless or a smart card though.
Also, what kind of gateline staff would glare or give a death stare for using the wide-aisle gate? That's just ridiculous, everyone is entitled to use it. I hope it was just an underpaid and bored worker who unintentionally gave a dirty look. I've had my own funny encounters at Liverpool Street such as exiting a gateline to check a departure board, and being let back through without presenting my travel pass before being shouted at (non-aggressively) by another member of staff. The first person explained it and it was all resolved in a friendly manner and a smile.