I don't have one myself but have ridden in loads on friends' horses. I love them and wish I would have got one myself (couldn't afford the last £100 so went for a Wintec Pro instead, nice but too flat a seat for me). They are quite deep and sit you in position, if you like being "held" in then they're great but if you like to find your own position then they might not be for you. The Wintec Isabells sell well second hand I believe, not sure about the Bates ones as I've never really seen them second hand.
The isabell is very secure, you can choose what thickness knee rolls you have. very deep seat and very comfortable. Would have one again. I think they sell for between £280 and £450 second hand.
The Bates I don't know much about, but the cantle looks less high and flatter.
Personally I love being sat in a deep saddle.
Albion do a smiliar saddle to the isabell and are reasonably priced on ebay.
I'm trying to find one to borrow for a test ride - they were suggested as an easier to find second hand saddle as I particularly wanted a Kieffer Action after riding in one of those
I had a wintec Isabell and sold it to a friend for £300 with synthetic leathers.
It was in good condition and I loved it but it wouldn't fit my new horse.
I bought the Wintec Isobell Worth last week from my Saddle Fitter for £595 (no leathers etc). He threw in a pair of extra deep knee rolls for me too. It has changed the way my shire goes completely and he is very happy in it
My OH took a sharp intake of breath and said it's alot of money to pay for a plastic saddle
As I understand it the design is the same for both saddles the difference is the materials they are made of, the Wintec being synthetic and the Bates version leather.
I had one for my big chestnut horse and loved it on him, it is very deep and came with two sets of knee blocks. For the price they are new (about £1200) I didnt think much of the workmanship. I sold mine on ebay and got about 2/3rds of its full retail value back! It was in fabulous condition though, you couldnt even see where the stirrup leathers had been. Was suprised at how much I got for it as didnt think there was a huge market for them.
If you can find one to try I would advise you do that, as others have said, they do not suit everyone, I would not have one now as would find it too restrictive, on the horse I had mine for though that at the time was a bonus!
MrsT - yes they are the same saddle one in leather one in synthetic suede. I'm lookign for one to test ride but if I don't like teh Isabell it'll be the Kieffer action which I loved and fully blame Twiggy for introducing me to.