You need to establish if the seller of the flat is really "also the freeholder", as you say in your OP, as that would be highly unusual in a block of 8 flats. What's much more likely is that each leaseholder has an equal share of the freehold, which is very common, and that the seller will sell you their share of the freehold as well as the leasehold title.
Self management via a management company of which each flat owner is a shareholder is preferable to having an external freeholder imo, as freeholders come in two flavours generally - those that maintain the place properly and expect to make a profit for their trouble, and those that don't, which is bad for the building long-term. With a share of the freehold, everyone has a vested interest in maintaining the place but no one wants to pay through the nose. They are also generally in situ unless letting out to tenants, which makes meeting to discuss management of the building is easier. If all leaseholders have a share of the freehold, then renewing a short lease is generally a formality, whereas a short lease is a catastrophe with an external freehold (and would greatly reduce the value of the flat and the offer you should make).
You can perfectly well budget for maintenance without an external freeholder. As a purchaser, you will get accounts showing amounts paid over the last however many years, and your solicitor will enquire about known upcoming costs, and you just put enough away each month so you can afford it when it's needed. As a joint freeholder, you'll also get a say in what work is done, when and by whom. You do have to hope that everyone will take a similarly grown-up approach to it so that necessary work doesn't get postponed, but tbh being slightly at the mercy of other flat owners is part and parcel of only being able to afford a flat instead of a house.
The agent or the seller themself should know most of the answers to these questions so you can weigh them up before deciding if you want to offer. If you buy it, your solicitor will get chapter and verse.
Not having a go at you personally, but I don't really understand how anyone gets to the point of making an offer while still saying things like the flat is marketed as "self-managed" or whatever that means. How do you know what to offer if you don't actually know what you're buying, what it means or whether it's what you want? You need to ask these questions and make sure you understand the answers.