You make a good point about trial-and-error - I should include a preview so you know what the fusion will look like / what its stats will be, before you pick whether you'd like to buy it or not.
Fused Hoobagees will almost always be stronger than both of the components that make them. Antifused Hoobagees have a 100% guarantee of being at least as strong.
The level of the fusion/antifusion is not actually a good indicator of strength: if you antifuse any two Hoobagees that are the same level, then the antifusion will have the same level as both of them, but its stats will all be better (and possibly much better, depending on what Hoobagees you antifused).
Fused Hoobagees will almost always be stronger than both of the components that make them. Antifused Hoobagees have a 100% guarantee of being at least as strong.
The level of the fusion/antifusion is not actually a good indicator of strength: if you antifuse any two Hoobagees that are the same level, then the antifusion will have the same level as both of them, but its stats will all be better (and possibly much better, depending on what Hoobagees you antifused).