If you are considering buying an older model SIP then I would advise you to do a search on this forum and read up on the model, they are not the most popular machine and can be very troublesome with the wire feed.
They can however be modified and some members have got them sorted and appear happy enough with them.
if all that the problem is the wire feed then pick one up cheap but go for gasless and gas clarke hold there money so take note
if the mod is all thats needed then you have a bargain
I echo what gaz and steve say; out of the box they really aren't great (and I say this as a happy SIP owner).
But, if you can get a 2nd hand one cheap and are happy to spend a bit of effort and money on modifying it, you can actually get a strong machine for not very much money.
A side effect that Land Rover owners will empathise with is that having to learn how it all works and how to modify it makes you far more knowledgeable about how the machine works!
Just modified my old SIP Migmate 130 turbo with the metal strap that keeps the tensioner and driven feed wheels vertical. Got some smooth welding done today on the subframe. However the mig wire kept binding in the liner and I didn't have a spare so sprayed mig wire with anti-spatter spray and problem vanished. Didn't affect welding quality either.
ive moded both the sip 130 and 150 gasless/gas with the strap gonna first try the welds again and consider the other option of the seperate power supply for the wire feed
i like the sip for the gasless option but do like the gas version as im inside anyway