The only problem that I might have with such companies is the tendency to "bump" work.
It can be irritating to quote for work or to lose work to companies that miss windows while regarding that as part of normal service. Also, some of the seemingly less critical H & S stuff may be skimped or left out completely.
I do clean all the windows for which I quote (if that's not possible for some reason then I tell them) and I do try to carry out H & S stuff in a responsible manner. Additionally I make a decent effort to scrub and rinse properly (particularly on lower frequency work) which can make me a bit slower than some.
I'm not saying that UK Commercial Cleaning either bump work or skimp on H & S. I just don't know enough about them to say such a thing. However, I do know that it happens quite a bit in our industry.
I have some larger jobs where I could reduce the price and do them in less time. However, I wouldn't want to put my name to such work. Nor would I wish to skimp on the 10- 15 minutes it sometimes takes to try making trailing hoses etc safe for the public. Obviously you can't cover everything. I've even had someone walk into me while I was cleaning a shop front because they were walking along playing with their mobile. I've also had someone trip over a warning sign. However, you have to try to be responsible and that can add time to a job.
I doubt that I have too much work that the big boys would be interested in but there are some jobs that might catch their eye.
So long as they don't bump work or skimp on H & S, then good luck to them. That's business.
If you employ a load of people it can be possible to provide the service more cheaply than a sole trader because the margin on an individual job is far less directly connected to the wages of the boss. The boss only needs a small margin on each job to live well from them. I suppose it's a bit like the corner shop versus Tescos. However, the quality of the service can suffer badly if adequate controls are not in place.
Currently I prefer to do all the work myself to ensure, as well as I can, that I give a decent service and earn OK from it. That may not always be my business model but for now, it's the one that is best suited for me.