Pros
The atmosphere is always friendly and positive.
There is a good social scene: pub every Friday lunchtime; company subsidised trips to go-karting; people go out and cycle together at lunchtime. The company pays for partners to come to the Christmas party, etc.
Officially, hours are fixed 8.30-5.00 with lunch 12.30-1.30, but in practice there is a great deal of informal flexibility arranged verbally with your manager. There is no expectation to work more than your contracted hours (although some people do).
Annual appraisals are a bit laborious, but they are fair and if you list something as a personal development target then the company will help you to achieve it through the year.
There are showers on site but there is nowhere to put your towel. There is a microwave and free bread and fruit in the canteen. There is a cupboard full of pot noodles etc that are charged at 50p deducted from payroll.
Overall I enjoyed my 5 years at Irisys and would recommend it is a place to work in engineering (but maybe less so in management).
Cons
Irisys was founded as an R&D driven start-up, where every penny was ploughed into developing cool new things. When they were taken over in 2012 by Fluke Corporation this changed so that every decision was based on whether it would make money for the shareholders. Staff that have been there a long time moan incessantly about this, and although there is a bit of corporate red-tape, it is nowhere nearly as bad as many other places and this shouldn't put you off.
The mezzanine where the R&D staff are based is too noisy and sensitive types might find it hard to concentrate.
Salaries are a bit lower than a competent person might hope for elsewhere.
Officially, pay-rises are performance linked, but in practice everyone I asked got the same as me: 2 or 3 percent each year. There are no bonuses for the majority of staff.
Project-based targets are set by the parent company and are always totally unachievable given the limited resources available. If you don't like always being late then this may stress you out. If you just accept that the targets are nonsense to begin with then no one is going to shout at you for not meeting them. The Technical Director does a very good job of deflecting this kind of thing from the people beneath him.
There is quite a high turnover of staff, which is mainly caused by people leaving to get more money elsewhere rather than anything about the day-to-day job.
While I was there they did terminate two people at the end of their six-month probation. One I thought was fair. The other I thought was a bit harsh; they shouldn't have expected him to be amazing given the lower-than-average wages offered.