So I've been thinking about the pros and cons of ultimate evolving the Toy Dragons.
Pros:
Boosted stats
Benefits from boosts to both elements
Can hit twice (useful against high defense/low HP enemies)
Better for multi-color teams, e.g., Chinese or Egyptian
Appease OCD players who must have the highest form of a monster
Cons:
Introduces a second color that can be potentially bound
It would seem like the pros outweigh the con, but some people really think that con is a deal breaker. So, I thought about the color combinations and how often that secondary may be a liability. I think the times it'll be a detriment are really rare.
Here's a look at each dual-colored Dragon:
Flare Drall - If using against a Wood boss, Fire is likely to get bound. If using against a Fire boss, Water is likely to get bound. So secondary green element is inconsequential.
Megalodran - If using against a Fire boss, Water is likely to get bound. If using against a Water boss, Wood is likely to get bound. So secondary red element is inconsequential.
Fortoytops - If using against a Water boss, Wood is likely to get bound. If using against a Wood boss, fire is likely to get bound. So secondary blue element is inconsequential.
Angelion - If using against a Wood boss, Fire is likely to get bound. If using against a Light boss, Dark is likely to get bound. So secondary green element is inconsequential.
Drawn Joker - If using against a Water boss, Wood is likely to get bound. If using against a Dark boss, Light is likely to get bound. So secondary blue element is inconsequential.
Sure there are still some cases where your secondary element will be bound (such as against enemies that can bind any color, like Mystic Masks and Mythlits), but those are relatively rare in the dungeons you would need to use the Toy Dragons for. And even then, it could be a good thing instead of a bad thing, since the secondary element can be used as a shield, drawing the bind to itself, instead of getting your whole party bound.
So, in short, I think the fears of having a secondary element that can be bound are overblown. And I think the pros are worth ultimate evolving the Toy Dragons. If it helps one to make the choice, you can also think about it as gaining an easy 40 or more +eggs.