There's absolutely no need to use an estate agent if
(a) you can find a way to advertise the property for sale ; and
(b) you (or a friend) can be present for any viewings that will be required by potential buyers.
When I came to sell my late father's house I realised that it was on a main road and close to several other properties that were for sale. (So anyone viewing those properties would be likely to notice 'For Sale' signs on my Dad's house). I simply designed a suitable sign on my computer, printed it out and took it to a copy shop, where I got two A2 copies made on brightly-coloured paper for about a quid each. I then put those signs in the windows of the house. Result: One successful house sale at a cost of just two quid (plus, of course, the legal fees)!
These days you'd also need to get an Energy Performance Certificate for the house, so that would add a bit to your costs, but there's definitely no need to use an estate agent if people will be able to see that the property is for sale.
When selecting any estate agent though (irrespective of whether it's a traditional or web-based service) the important thing to check is which websites they'll advertise your property on. Many people probably look no further than RightMove, Zoopla and PrimeLocation when looking for a house, so it's important to check that your property will be listed there. (Annoyingly, you can't go directly to any of those sites; you have to go via an estate agent). As long as your property appears on each of those sites it's unlikely to make any difference as to which type of estate agent you used to get it there.