Pros
The work is varied and interesting, and you're given a lot of responsibility and freedom early on. The people are genuinely very nice, and the office environment is friendly. You get a lot of very marketable experience very quickly - stakeholder engagement, specifications, UAT, etc. These all look great on a CV (which you'll want when you decide to leave after 18-24 months like everyone does).
Cons
The salary is uncompetitive, especially after a few years in the role - after 2-3 years at Acturis you have more than enough experience to be applying for roles in other companies paying £55-60k, when Acturis will have you on (at best) £45k at that point. They claim to have a mathematical system for calculating salary changes, this ultimately boils down to an unquestionable black box they use to avoid any discussion about your pay change being unfair or insufficient. The workload can often spike for periods of up to a month when multiple projects coincide - there's no recompense for when you work over your hours (other companies which offer actual flexi time have schemes for repaying overworked hours like flexi balances, here you get nothing) The hours are long. You are contracted to 40 hours, but if you actually take your lunch break, you're doing 45 (9-6 every day). This is more than needed, studies have shown longer hours make people less productive. They claim to have flexi time - 9-5 with a "flexible hour either side" is not flexi time. The turnover rate is very high because of the lack of progression and the poor pay once you get experience - I am the most senior (excluding management) member of my team at 2 years, everyone above me (was 3 when I joined) has now left.