Hi there,
First of all well done for getting motivated to go back to "school", it's a big decision !
I am 30, and am studying 3 A-Levels via distance learning (specifically the National Extension College), 3 As predicted, and I am currently holding 2 offers for Vet Med.
I cannot say if A-Levels are preferred over Access to HE courses, that would be one for the admissions teams at the universities you want to apply to. (I do believe that some people on the forum have had offers from HE courses)
I will however say that A-levels include AS levels, so are designed to be studied over 2 years, whereas I believe AtHE is 1 year (fact check me on this !)
With regards to my own experience, overall it has been positive, I feel well prepared for 2 of my 3 subjects, the last one being Chemistry which I do not hold a GCSE for, so it has been a VERY steep learning curve (also, the specific textbook accompanying my syllabus is not very beginner friendly).
The website is very intuitive, all steps of the course and the examinations are clearly explained.
I have intensive weeks coming up for the practical part of the exam, everything is booked via the online platform (including the actually A Level exams, they have many partner centres around the UK).
In terms of drawbacks, I will say that it is expensive (all-in, around 1k per A level), and you have minimal guidance from tutors. You have assignments to hand in, with feedback, and sometimes they send a message to check up on you, but it's not at all the same as seeing someone face to face. This is not a problem for me as I work best on my own time, and have used a lot of internet resources to answer any questions I could have. (I could message my tutors with specific questions, but it's been easier & faster to look it up myself frankly)
You can however book extra tutorage via video chat, but these are a payable service.
NEC also provided my UCAS application with a reference. Obviously, I do not know what was in it, and got a bit nervous about it because they do not know me, and I wondered what they could possibly say, but it has not stopped me receiving two offers, so can't have been that bad ! It is a big show of motivation to study by yourself, so maybe it played in my favour, who knows !
That's the last thing I will say : it requires a huge amount of time & dedication. Remember that these are normally studied full time. I have personally quit my job to work on my studies full time (luckily, my personal situation has allowed it), and sometimes 8 hour days of chemistry is not fun, but I also know what I'm doing it for.
Anyway, if you have any specific questions, do not hesitate to ask, I wish you all the best !