Working on some new metamagic stuff for a game I am doing and wanted to get some comments about one of them.

Advanced Metamagic Technique

Imbuing
Prerequisite: Invoking (p. 57, SM)
Initiates with the Imbuing metamagic learn to enhance the unbound spirits they summon into great form spirits. An initiate must declare she intends to use Imbuing when performing a Summoning. The drain from the Summoning is increased by 50 percent (round up). If the summoning succeeds, the initiate immediately makes an Imbuing Test, rolling Magic + Summoning. The spirit’s Force is added as a dice poll bonus. The hits scored on the Imbuing Test determine how successfully the initiate transforms the spirit into an Imbued great form spirit and expands its natural abilities, as noted on the Invoking Test table (p. 57, SM) (except where noted below). If the Imbuing Test fails, the entire summoning attempt fails. An Imbued great form spirit cannot be bound.
When a spirit is enhanced into a great form with Imbuing it is harder for the conjurer to ‘handle’ then a standard unbound spirit and it is more ‘real’ in the metaphysical sense. This has two game effects.
Firstly, the magician has to dedicate some of his resources to keeping the spirit ‘in line’. The unbound imbued great form spirit counts as a bound spirit for the purposes imposing a -2 dice pool modifiers per the Bound Spirit sidebar (p. 178, SR4).
Secondly, due to the more powerful spirit a magician is controlling unbound, the bond is not reinforced as per the Invoking Test table (p. 57, SM). Replace the entry for "2 Hits" with the following.
“The spirit becomes more real when materialized or possessing a vessel. The spirit gains the power of Realistic Form (p. 102, SM)�

I don't think imbue is the correct word for this metamagic. You aren't really infusing or saturating the spirit with anything. Invoke is really just another way to say your a calling upon the spirit, maybe that would be a good direction to go for this metamagic name. If I were to have just heard of a metamagic called imbue, I would think it would be something similar to the quickening or anchoring metamagics.

The metamagic is actually worse than invoking because you have taken away any of the advantages one could have from not binding the spirit. You are also going to have less services since you are not binding the spirit and won't be able to use bound services. You also added in a -2 dice pool, that is normally just an optional rule. Not only that, but you go through all the trouble "imbuing" the spirit just to have it go away at sunrise/sunset. The only people this metamagic will appeal to are those without the binding skill. I certainly wouldn't get this metamagic if I already had invoking with a binding skill.

I would take off the restrictions and remove the prerequisite as well. It isn't even close to being an improved version of Invoking.