Hey! I'm currently on the same course and I'm two units away from completion, currently holding two offers with Southampton and Cardiff.
The course itself is pretty intensive and is quite Maths heavy, it covers a few A-Level topics (i.e., Calculus, Binomials, Trigonometry) plus engineering mathematics, so definitely be prepared for that. I had retaken my GCSE Maths just before starting the Access course, as I needed the grade for University and I hadn't practiced it for years, I found that it helped a ton in terms of relearning the fundamentals before moving onto the harder topics. The course obviously does teach you this but going back to revise certain topics might help.
In terms of how long you spend on the course, each unit is spaced out so it lasts about a year, with about 20 days per unit (tends to vary). BUT if you're planning to apply to University the following year, you'll need to complete by the 30th June at the very latest, so I'd recommend starting the course as early as possible. There's also a deadline for the 22nd December to get your UCAS application in for processing to meet the equal consideration deadline (altho admittedly I missed this by a couple weeks, and they still processed it in time!).
There is tutor support, although it's a bit limited - you can only submit drafts up to Unit 9 (which I had no idea about before starting?!) and afterwards you can only submit your work once. Admittedly I haven't used tutor support that much, so can't comment on it overall, but it's something to look out for.
Overall there's a huge emphasis on independent learning: the first four units will introduce you to the course, teach you study/essay-writing skills, etc. but honestly there's not much hand holding at all. You'll definitely need to be disciplined when it comes to putting in the work, but it's pretty rewarding if you can do it!
Happy to answer any Qs about it if you have any!