I have a Marmalade Car and like you, up until a week ago I was an Apprentice and to complete the quota of being just like you, I bought the ST-Line Fiesta. Bonus points for the fact they could only give cashback for my insurance too
It's risky, you're locked into a long credit agreement and if you lose your job, don't get offered a full-time role (as what ALMOST happened to me) or you crash the car, you are so screwed. I'm also probably going to have to buy the car at the end too, I can't abide by their mileage limit lol, I like my girlfriend too much.
The buying process was very easy, but the problem is you don't get a direct line to the dealer. My car is missing some features I feel like I should have been given as stock (courtesy lights for a bloody start) and this is largely because I couldn't tell the dealer what I want, Marmalade just get their discount, pay up, and have the car sent to you and that's that.
Also in fairness, you're better off not being insured by Marmalade, take the 1300 or whatever and put it towards a decent policy, even if it's like 2700 unboxed the 1300 takes the sting off it. Technically my insurance is 800 quid this year (but it's really like 2200, let me enjoy things).
Just understand the contract, what you're getting yourself into, include the fact you're slightly overpaying for a car as well as the fact that whilst cars don't depreciate in value like they used to, you'll probably stand to lose £5000 by the time your contracts up (which is usually covered by the balloon payment) and if you don't buy the car at the end at all, you've chucked like 10k lol, so wanting to keep the car in the long-run is an obvious must.
Any other questions let me know as I've been through the whole process.