Nice water Hyacinth! IMO, pretty nice score.
Got one in my 5G, but the plant's pretty small.
For me, it grows slower than nearly everything else I have.
True, many people would say it's not worth the risk and you should take it outside and burn it.
I'm not neccesarily one of them... I got mine from a "wild" fish pond. I did get end up getting some little critters from them, but they were harmless. (2 little invertabrate species were swimming around my tank for a while... one was a little worm that crawled on the sides, and the other was a little speck that swam around the tank. I introduced a ghost shrimp to the tank and he ate every one of them within a day. lol)
Just balance the risk and decide for yourself if its worth it. Chances are pretty slim that it is carrying something, but it's possible. If you let the plant stay in your tank without any fish at all for a month or so, then that would likely eliminate any parasites that could be on it, leaving bacteria and viruses if any.
A healthy fish could probably fight those off even if they did get carried, and it's also pretty likely that the plant is covered in infusoria (bacteria and microorganisms that are harmless) which could seed your tank for any future fry born in the tank.
If you leave it in afishless tank to QT it, I think it would be relatively safe. (again, decide for yourself if its worth it. If I was keeping discus, I wouldn't have done it. I put it in a tank full of snails and ghost shrimp- if it infected all my inverts, oh well I'm out less than a dollar. lol.)
just my 2 cents, take it for what its worth. Which is 2 cents.