I can't say much, which is a poor way to start this answer, but I will give you my impression. I have a generic green dissectum grown as Viridis and a maple sold to me as Green Mist. I think that Green Mist and Waterfall are very similar, as they will be to Viridis. You will see a mounding maple much wider than tall in time, and if you don't view them at the right time of year, you might not be able to tell them apart. Those are strong growers that take sun well and will probably display a good, if not stunning primarily yellow and orange fall coloration.

I have seen Green Hornet in late spring and summer now for the last two years and have not yet purchased one, but it is one my list. It is not as lacey and graceful as the other two, but the leaves are held a bit more stongly in the petiole and it is supposed to achieve a very good red fall color which is different than most green dissectums. Will also see the leaves edged in red or rust for a good portion of the year.

While not as easy to find, I think that Green Hornet is a very good selection. There are some mix-color green dissectums that are also very good choices. Baldsmith and Watnong are great and Chantilly Lace is a newer one very close to Watnong. I also just picked up a Filigree Rouge which is very nice and Emerald Lace. You might also add Lemon Lime Lace to the list for a very fine leaf with stron yellow tones.

When it comes to the green dissectums it is best to see them in person to decide. I like to see them in spring and fall when possible. It is also helpful to study them before buying if it is important to you as they get mixed up pretty regularly.

Hope that helps,
Michael