I think the novice only days would be good for inexperienced drivers, especially if instruction is free, you get cones marking turn in and braking plus apex points so very useful. Then you can usually get pay tuition on an open track day. You'll get less time perhaps on a novice 'session' day because you have to be ready and in the queue at the right time, so if fettling the car for example, you could miss out. This can happen as you may still be checking or repairing the car, which should be checked at every return to pits.
The open days can be daunting. I've not done many really, maybe 6 or 8, and still have been on with a mix of stuff at Oulton and Ty Croes on Anglesey, or the 'Ring' which is something else. I have sat in on many more. I think anyone will get more from an open day unless you're not used to driving fast in general. If you're not confident at speed and manoeuvring at speed combining braking and gear changing while adhering to the correct line and braking and turning zones likely to be essential on a track etc. Then the novice day will work for you if you need to be guided for what and when.
Don't be put off by the speed at which things pass you as a spectator, this is what bothers me initially. Then look at the cars perhaps, when you see it's a stripped out (often not) fiesta, Mini, Clio, E30, it isn't hard to realise the top speed at which they're passing you might not be that high. Even much faster looking cars aren't going 'that' much faster 'in general' and when you're out there, they will pass you quite safely and quickly on the side they're allowed to, and nobody in general can overtake in the corners, so really there isn't much to be afraid of.
The most important thing for novices to keep on top of, is use of mirrors, and indicating as soon as a faster car appears quickly in the mirror. They will be on your tail soon and cannot pass in the corners, so courtesy is valuable on track. There will be blue flags usually anyway, but if you decide you want a race with them when you're clearly slower, don't. You can get reported for not moving, and called in.
There will be places a car gains on you which could be one particular straight for instance, but the time will come where you may legitimately hold your ground once used to the car and track, knowing you'll clear off at the next bend, you may have done this over several laps and made a small error allowing them to close on you but it doesn't mean they're faster and should pass. The safest way though, and least frustrating for the other driver if they're all over you now, is to let them pass, and you can always get back past can't you. That way people don't get wound up. Believe me tensions get high, the adrenalin can take hold. So you do need to be strong enough to say to yourself 'it's ok' haha. Take a breath, or even end the session for a walk around. Red Mist can cause some problems for both, it's hard to recognise sometimes.
Sit in with a helpful driver to get an idea of what's around you, and on another lap focus on what they're doing, so see that they get in the right gear before the middle of a turn for example. Set the car up for the turn, and drive through it. It really doesn't matter if they use heel/toe and you can't do it or wouldn't know how. What matters is that you are in the right place, getting the car to the right speed before you change direction at speed, and get in the right gear however you're comfortable, to be able to pull out of the turn, you'll see what gear they choose.
Some track day goers use too low a gear anyway. The Cooper S has a good pull and can deal with 3rd over 2nd in a lot of corners so don't worry about changing down several gears if you're not used to this. Much of a track for those that haven't been, will be, or 'can be' done in two gears, 3rd and 4th typically. 4th on the Cooper S will take you to around 105/110 vmax, not many people change up from there because they'll be getting out of that gear any second, so they may hold on to it for a few yards. Others might for various reasons, I may for example, to help reduce intake temp, or some corners I may take in a higher gear.
It would be nice to meet some people from here, my experience on MT is that most members live down South haha, so I won't travel that far I don't think, although I do want to drive Brands Hatch. I won't go down there for a novice day, I think it'll be a waste of money. Unfortunately I'm not too keen on old industrial estates or aerodrome tracks, I'd rather go to a proper venue, part of the experience and value for me.
Those wanting a weekend day will pay through the nose for it.