Have two aubergine plants and the fruit are 4-5" long. I picked one as it looked like it was ready to fall off, and tried it last night.
It was full of seeds, and tasted horrible. Have never seen seeds in the ones you get in the shop (apart from the odd one). What could be wrong with them?
They get seedy and a bit bitter if they are left too long ripening . I find they are best picked when really shiny and firm. Perhaps your other one is younger and yummy.
Sounds very much like you let it get too ripe
Aha..that explains it. As the fruit are still small compared to supermarket ones, I thought they had a couple more weeks to go before they were ready!
Expensive compost >:(
A few of mine were quite seedy but ok to eat. I noticed a couple had gone from purple to an almost brown colour - definitely gone over and as you say expensive but nice compost !!