Pros
They're extremely good at "hiring smart" - their developer hiring strategy is entirely based around hiring intelligent graduates which will be able to quickly adapt, learn, and rapidly grow as they're thrust into positions with lots of responsibility very quickly. This naturally results in a team of super bright individuals, everyone is young and fun and I still meet up with many of them regularly despite all of us having since left the company. This "sink or swim" environment definitely isn't for everyone, but if you're good at self-learning and are able to "swim" successfully when they throw you straight into the deep end, then you'll grow extremely quickly as a developer. I personally found that it accelerated my learning and growth so much better than anything I could've got by being a "small cog" in a large established tech company. I had a positive experience overall and really benefited from my time here (hence 3/5 overall as that's above average), but please read the cons section - this environment really might not be for you.
Cons
The fact that they only hire graduates means that there is very little guidance from more senior, experienced developers to learn from. Once you've been there for a year or two you'll likely find yourself being one of the most experienced members of your team with no clear direction for career progression. No-one stays for much longer than two years, and management clearly has no idea what to offer as motivation to do so beyond just throwing more money at you. The company is already relatively successful and has some very powerful investors backing it, yet still like to pretend as though they're an early stage startup. The CEO once gave a presentation to the tech team likening us to the "first 20 Google employees", with a focus on making it clear to us just how rich we could get as the company continues to grow. Needless to say, this company isn't and won't be Google. The speech felt extremely disingenuous (we already had many more than 20 employees regardless!). I'm sure some people will get very rich when Luminance eventually sells or goes public, just look at its big brother company Darktrace (or - god forbid - Autonomy's sale to HP). However, those people aren't the young graduates they hire as starry-eyed developers and massively overwork, squeezing much more value out of them than their meager graduate salary would imply. As that last sentence hinted at, a big feeling I am left with after leaving Luminance is that of having been used. I got hired cheap, adapted quickly, took on responsibilities I wouldn't have ever had at any other company, and I provided massive value to the product without the company ever really giving me much in return. Don't get me wrong, I learned a huge amount. As as I said in the pros section, it made me a much better developer - my career got a massive kickstart out of it. But it's not like any of that was intentional growth and development provided by the company. I know several people that did not adapt well to Luminance's "sink or swim" approach, were never provided the proper training resources and guidance to grow, and as a result had a miserable time at the company. Make sure that's not you. A big reason for my leaving towards the end was that as I got more exposed to higher management I realised just how much of the company was micro-managed by its largest investor (again, look up Autonomy to find out more about the character) and how much of a culture of fear he had built at the top. Not fun. Tech wise, the code is riddled with tech debt which isn't properly addressed by those in charge. Luckily us devs were very passionate and constantly working to improve things, but when you only hire graduates with little programming experience you're naturally going to produce a lot of bad code. There's absolutely no code review process, which clearly doesn't help. There was little to no testing when I arrived (has improved a bit over time), and virtually no tickets or time assigned to clean up painful areas of the code to avoid future issues.