I think "Merge" is used when you want to sum/concat/mul two Sequential() models. The "merge" is used when you are working with functional API. However, this is not written anywhere in the documentation. Additionally, Sequential documentation has a section called the "Merge" layer, but ...
I know this is a bit late but in your ama in march someone said that you (ninjakiwi devs) are not happy with the state that btdb1 is in and that's why you don't really advertise or try growing it. What are the reasons for that and if you can say what you are changing in bt...
V3 is also looking to improve the buggy yet impressive particles currently employed with newer ones based off the old particles used in 2007 TF2. The change mainly is towards the flamethrower which had a very obtrusive particle effect that really didn't fit with the hitbox of the weapon ...