Spirit's use of Edge depends only on the GM's will, that's all. But of course, if the GM allows the spirit to use his edge each time the summoner needs it, it may occur little changes in game balance.
I know very little about technomancers, but as far as I know, they can too fix permanently these skills with a ridiculous karma cost, and they're still able to thread them in order to up them if needed.
And anyway, if you can summon such powerfull spirits, then with a task or guardian spirit in a possession tradition, 18 to 20 dices is the minimum you'll roll when using the skill. Far above what you'll get with the spell.
I don't say it's a bad use of the spell, it's interesting, but considering the summoners' abilities (wow, no drain from a 9-10 spirit, without edge it means an average pool of 18 to 24 dices, nice stats !), it's far from "very powerful".