My display fleet is all originals but the fleet I game with is all made of Recasts. Same with the chaps I play. It's not like we can go and buy new models anywhere so we are forced to go the recast route. If GW brought back the BFG range I'd just remortgage my house.
I mainly do the recasting myself. It's not great but it will do for gaming pieces. I have ordered 3 Battleships off AliExpress before and they are pretty hit and miss. Some parts are fantastic and some parts are rubbish. I only got a reply to my complaint when I threatened to leave a bad review so the customer service is also a bit hit and miss. I did build my Dreadnought out of them though so it's not like they are unusable. Just not if you are OCD on quality.
Having said that, I bought some Marine Novas off ebay that came from AliExpress and you can't tell the difference between them and original FW ones.
As for "is it worth it". It really depends on what you are trying to cast up. Silicone and Resin aren't cheap and the postage is expensive as well so you have to be quite committed to doing it. If you haven't done it before it can be quite hard making the moulds and getting the resin mix right. I've had it a few times where I haven't mixed the resin correctly and just had to ditch the cast. The same goes with the Silicone actually - but that was only once!
I'd also limit yourself to only doing simple models as well. One or two parts at most. I mainly just cast up escorts as cruisers tend to require a LOT of resin and the detail is very hard to capture if you don't have access to a vacuum chamber.
That post was a lot longer than I meant it to be....
If you want tips on how cast stuff up yourself, just ask. Otherwise, go for AliExpress.