Pros
Working hours are actually as described (9-5:30; half hour for lunch). Very few people stay longer. 27 days holiday per year (plus 8 bank holidays) as of 2014 (3 must be taken between Christmas and New Year). Good internal personnel website - search for anyone, with photos and job titles. Very good budget for buying tools and equipment. The work is very interesting and varied. No dress code! Very well equipped workshop, and easy access to advanced prototyping capabilities. Nearly everyone is friendly and easy to work with.
Cons
Huge open plan "office" (warehouse really) is quite loud due to all the nearby vacuum cleaner testing. It can be cold in winter. You can't carry any holiday over New Year as of 2014 (most companies allow 5 days). Parking is horrific. Traffic when leaving is also bad (everyone leaves at the same time). Getting a seat in the cafe is nearly impossible. This is due to hiring many new people recently. Salaries are not transparent at all.