Please do a thread search as I have commented before - however:
1) Size is an issue, especially with untrained staff (don't lets start that issue in this thread!). For years you could get a 600g aerosol BC Powder, but now the pound type bargain shops sell a chinese 500g ABC Powder from the '1st Aid' brand of household medical & safety supplies.
The discharge time is very short and to maintain a minimum time the flow rate poor.
300g extinguishers are manufactured, but aren't seen much here (yet)
The problem with a lot of the smaller extinguishers is that they are BC Powder, not ABC and many end users don't realise the difference and have an extinguisher that is not that good on their main fuel type (go on youtube and you find a clip of a 6 kilo BC struggling on what would be no more than a 5A test fire)
I would have ideally set a minimum capacity/rating of 1kg/5A:34B or better 2kg/13A:55B.
2) Servicing. The original aerosol extinguisher as pioneered by Firemaster (now part of UK Fire) was made in sizes up to 2kg & 2 litre was totally unservicable other than by checking the safety seal & weighing (both a user could do). As a result they were marked with a 5 year warranty and it's function would not be guaranteed by the manufacturer after this date. To encourage replacement Firemaster would give a 50% discount on exchanging an unused out of date unit.
In the late 80's pressure gauges were added to some models of at least 1kg/litre so that they could be kitemarked to BS5423 rather than BS6165 and thus be acceptable in workplaces and on transport where BD5423 compliance was required. Being non refillable they still had the 5 year life and no service requirement.
The guidelines follow this principle above.
HOWEVER
We know that the Govt guide writers have traditionally been 20 years behind with extinguisher technology and this is the case now.
Genuine non refillable aerosols as still made by Firemaster & Fireblitz (new firm set up by ex Firemaster staff) would come under a 5 year life, service free, principle.
But the following types sold directly to the public in stores are different:
Kidde range of residential extinguishers: Are actually standard rebadged Gloria BS EN3 powder extinguishers as you could buy from any extinguisher supplier, are refillable, requiring Basic & Extended Services
First Alert: Rebadged 1kg ANAF EN3 powder - again refillable, needs BS & ES regime.
1st aid: Standard chinese powder can & valve as used by people like Firex, Jewel ,Excelsius, etc just in a small 500g size. Refillable, needs BS & ES regime.
Guardian/Vanguard:All now refillable, needs BS & ES regime.
I could go on.....
The basic principle is that unlike say 10 years ago, most general sale extinguishers are not now disposable, maintenance free aerosols, but standard 'industrial' refillable, requiring the same maintenance as their larger counterparts