Lumo

No but there are reviews on Facebook or have you seen them?

https://www.facebook.com/LumoTravel/reviews/?ref=page_internal

I haven't used them largely because I am still very Covid cautious, and with only 5 car sets, their business model requires them to be always near 100% capacity, so I choose my routes, times and trains carefully to avoid crowding, but I stress that is just me being somewhat neurotic.
Living in the UK I am not aware that they are any better or any worse than any other train operator.
Yes the food offer is a bit odd- you have to pre order and they buy it in from major supermarkets or take out stalls. That is clear on their website. They only offer quality food so as long as you can read a website and comply it works. This is cost effective for them, no dead stock.
They use the same type of trains with the same 'ironing board' hard seats as LNER or Great Western, and like many trains skimp on luggage space.
If a train is cancelled due to their problems their wide spacing of service will always be a problem. The trains are new so aren't failing all the time. But if it's cancelled due to an infrastructure problem like overhead wires down, signalling problems etc then industry wide standards of inter-availability mean you will get transferred to another train operator. Or buses/taxis summoned if the line is blocked with no diversionary route. But buses take time to resource.
Facebook reviews will always focus on the negative. You would see the same for LNER or National Express- read Nat Ex facebook and you would think they are perpetually Greyhound on a bad day.
I see Lumo as the Easyjet of the East Coast main line. They get the job done, take you from A to B at a good price (and sometimes faster than LNER), but don't expect luxury. You want British Airways standards and a higher frequency service, travel on LNER. But on a bad day LNER will be just as hopeless as Lumo or as the much maligned Avanti. I can promise you that.
In short travel Lumo knowing what you are going to get, don't over expect. There is nothing inherently wrong with them.

Geoff Marshall, a transport and train vlogger made a video on Lumo when it started. It is no frills, designed to eat into the airline business between London and Edinbrgh so on the East Coast only. If you go in knowing you are going to get a budget service the reviews are very much that it does the job on the tin.

Thanks for your comments. May fly instead!

Unless you are at the airport, the train will be faster and easier.

If you aren't happy with Lumo (although not fancy or frequent it does do what it says it does) LNER has both fast and frequent trains to London from Edinburgh.

Geoff Marshalls YouTube is fantastic.
"All the Stations" in particular and Corrour being the " ultimate tick"
Bloke was smitten with the scenery