The reason London Info is what it is is because of funding.
Employing FISOs is cheaper than employing radar qualified ATCOs.
The UK has an ICAO obligation to provide an FIS and it does that. There is no obligation to provide a radar service.
An ICAO compliant FIS can be done by a man sitting in a hut with a radio
If many more people "used" London Info then the service would instantly collapse, and would be unworkable long before that because the same frequency covers such a wide area.
I never use London Info when flying normally. The only time I call it up is to get a handover to London Control following a departure from somewhere where the tower was unmanned, or equivalent.
A listening watch on London Info is a good idea IF there is no radar service available from somebody else. For example it would be daft to be on London Info when you could be talking to Farnborough
and this is true even if F is busy and can give you a Basic Service only i.e. no official traffic info.
On my one visit to London FIR at Swanwick, their radar display was filtered to ONLY show 1177 codes
That's funny because on my one visit to Swanwick, c. 2 years ago, the man told me their radar display shows all squawks
BTW I have a feeling that visits to Swanwick are all but worthless now because you get only as far as a conference room, whereas at West Drayton they actually showed people around the place.