We have been using i-Salon for just over 2 years. I chose it because it is geared towards the UK market so we don't have to learn the "Americanisms" - a real bonus. Everything works OK in the form that we have: bookings, sales, client database, stock control. It's easy to use the main features (bookings, sales, cashing up) and it includes text message reminders (but most systems do these days).
My 4 main problems with the system are:
1) It's proved to be more expensive than I was first led to believe (purchased on a cold call from a very clever salesman). For the most basic form of the system I'm paying £168.66 per month for the equipment lease and £124.57 for the software licence and support. (£3,518.76 a year!) There's no way round the licence because you have to input a new very long and complicated code every few months - the only way to get the code is to phone and then wait for them to check that your payments are up-to-date.
2) Technical Support is good when you eventually get to speak to someone, but you have to wait for an "expert" to call back and they only work 9-5 .... so not much use when you have a problem on the evening shift!
3) Excellent communication and advice in the first 3 months - then nothing. All they do now is collect my money!
4) The structure of the reports and database analysis is too rigid - if you want something other than what they provide you either can't have it or you have to pay a fortune to get them to program it in. Most of the standard reports/tables/graphs are poorly laid out and contain many errors. It's possible to output the client database in a format that can be read by Microsoft Word, Excel or Access, - that's OK for me but not much use for most.
If you don't need the easy to use booking or cashing up systems, then I'd recommend using your own database for client contact records and something like Sage Instant Accounts and Payroll for your admin stuff. The Sage products are far better designed and supported (although no need to pay for support after you've got used to them). A one-off reasonable payment for reliable, well thought-out accountancy and payroll software is far better value than something that has limitations and you have to pay for throughout its life.
I did try out Salon Iris and apart from it's American bias it looked much better value to me. But of course I have far less experience with it.
Hope this all helps.