If you want my pennysworth, it's this;
Yes it is possible to put your own system together from bits and bobs off ebay, but in my opinion it is a false economy.
I know people who have done that and they go on and on about how much money they've saved. But then they also spend a lot of their "working" time faffing about fixing problems. My opinion is that working time is like gold dust, you only have so much every week, you have to spend it cleaning windows not messing about with your equipment because it is unreliable.
And then of course there is the time you initially spend searching, buying, putting together, snagging etc your home made system in the first place.
I honestly don't know how those DIY lads can be bothered. Such a carry on.
I got my system from pure2o, which is ionics budget range. Can't remember exactly how much I paid but I think it was about £2,700 for a 400 litre hard water system plus a bit extra to have the van floor protected with speed liner (highly recommend that by the way).
They installed my system in the van, and it worked perfectly. It went on working perfectly ever since. Never had a single hour of downtime due to something not working. In my opinion, the sheer lack of faff is well worth the extra money, and crucially my precious work time has never been interfered with.
So anyway, my advice is forget messing about trying to build it yourself, just bite the bullet and get a properly made system installed. Life's just too short.
Problems? You don't get problems with a diy system mate, it's all very simple, nothing really to go wrong, maybe a small leak here and there,
The reason many can be bothered to do it themselves is becuase A - it's cheap, £700 for my whole setup
B - you know exactly where everything is and how it works
C - you have total satisfaction and knowledge of all the equipment
It's a no brainer, £2700 vs just £700
You won't get any more problems than anyone with a system put it by 'experts'
As for time, it really only takes a couple of days to fit a system, so that's a weekend, hardly taking up working time is it?
I looked at pure h2o systems before fitting my own, I just couldn't justify the money for what you get, it's cheap stuff mate, it looks nice in its wrapping and stickers etc, but it's all basic basic stuff, strip it back, it's worth less than half what you paid,
For two days work, much better to do it yourslef, you've then got all the choice of what equipment to use, total control over it all,
Best of all, the Mrs and I went to New York with the money we saved on a system, now that was worth it!