£40 for new ones or second hand? I wouldnt pay £40 second hand to be honest. I got 3 new ones for £11 new, including delivery. They were half price in a closing down sale. They are original ones though, so maybe you are looking at newer versions and they are more expensive. Jo knows more than me, lol.
The ones i have are like a terry toweling nappy, with a flap of terry toweling inside which is just like an insert, but is attatched at one end. If they are the same, then you also need a fleece liner, but you can make your own out of some fleece. I have that task to do toomorrow, lol. I bought a 120x150cm fleece from Asda for £2. Thats a lot of liners, lol. The fleece is because the material gets wet and stays wet next to their skin, but fleece doesnt hold moisture so it keeps their skin dry. They do need wraps as they dont have waterproof covers, so thats an extra expense to add to the £40. I got some motherease ones off of here 3 for about a fiver i think, so not bad. I also have some fleece wraps which im going to try out tomorrow night. The motherease ones are just like a plastic cover, so you can wipe it out and use it on the next nappy.
To be honest id say i use them less than my ebay cheapies. They have less bulk at the back than the Ebay cheapies, but more bulk everywhere else. For £39 i think...You can get 9 Ebay cheapies with 18 inserts.
Oh and i think any wrap will do the trick, as long as its the right size. The tots bots i have are sized, so check they are the right size or birth to potty x
ETA i have fleece wraps to try tomorrow, not liners, lol x