If you have found your way here you should be intelligent enough to know that these S16 machines are a rip off. Unfortunately I am not intelligent enough and as a Moderator here that is pretty embarrassing. Unless you have thousands of £ to waste avoid these and go shopping instead. Your money is better spent on stuff you can keep. Or beer.
Look on the bright side though - you did well to stop and walk away. OK, so forty quid might have paid for a night out or two, bought you a new pair of shoes, whatever - but you can move on and forget about it. Think how often you hear stories of people pumping well over a grand into one of these things and walking away with nothing?
You are right £40 is no great big deal but that took a couple of hours to earn and then 5 minutes in the arcade and it was all gone. Just annoyed with myself for being greedy.
Same as AWPs you have to wait for mugs to fill them up but it takes longer with SWP. In a week I can normally make 80ish quid if I go to loads of different pubs. But then those pubs are no good for another month. Some of the guys on here travel around and do SWP professionally so they can make £500 a week or more.
It's only beer money really for me.
I can't comment on the in depth legislative differences but I can tell you that a Section 21 machine must be restricted such that it can only be played within predefined 'sessions' e.g. 11am - 11pm. The machines I have worked on do not have different profiles as such.
I can only win about £2 on bully 
Im not being funny tka but how much cash can you make from swp a week?