I am thinking about getting a multifuel/petrol type stove ... what would be your advice for a simple and relatively cheap stove to buy. ...
Multifuel stoves are amongst the more complex types. If you want something which is truly multifuel (as opposed to the Coleman types, which basically use two fuels, both of which are more or less petrol) then try looking out for something like an older, e.g. second hand, European-made Optimus. I've had bad experience with the newer ones which are made in China. Although they may have fixed the quality problems by now, I'd still be reluctant to shell out over a hundred quid on one of them.
Strangely (it seems to me) some of the cheap Chinese multifuel stoves have been given good reviews here, check the archives, but I have no personal experience with them.
There are lots of cheap old paraffin stoves around, but IMO paraffin is as bad as petrol for smelliness.
After a long time not being able to find somewhere to buy "Aspen 4", I'm working with it at the moment but the jury's still out. It didn't work well in Shaggystu's Coleman Feather a couple of weekends ago at a meet in Derbyshire. I had planned to have another go with the Feather using other fuels but life has been in the way since then and I haven't had the chance.
Servicing of pressure stoves isn't usually too difficult when you get the hang of it. I much prefer the leather washer type of pump, in a pinch you can make a washer. The non-return valve seal can be an issue but a spare seal for that weighs about twenty milligrammes so there's really no excuse for not having one with you. I've used a total of one in getting on for fifty years of using paraffin and multifuel stoves.
Safety must always be on your mind with these things. A pressurized container full of fuel next to a red hot burner isn't something you want to treat carelessly.