initiation gets you a metamagic though, it doesn't get you to MAG 7 iirc? you'd have to then raise your MAG to 7 using karma. (pg 325, SR5 core)
So the total to get to MAG 7 without it would be initiation which costs 13 karma (and 1 month of downtime), plus 35 karma to raise the attrib. which is 48 total. if you're getting 5 karma per run then you're looking at 9-10 runs of doing nothing else with your karma and at least 1 month of downtime to initiate. Of course you could expediate it by trading cash for karma, but you're still looking at quite a lot of real life time and in-game time before you can get it.
I don't get where EDG comes in to the maths mate, i must have missed something...
if you're taking Human, 3 (priority D) and Magic A for MAG 6; then 1 SAP gets you to MAG 7 with 14 karma spent only on exceptional attribute.
your other 2 SAP get you to EDG 4.
Its a bargain really.
I get that using it on AGI or BOD or something is cool, but for a mage, its rare that i have enough attrib points to get my physical stats that high anyway, they go into mental stats for drain pool. I can def see the value in getting WIL 7 or something that you can't boost otherwise, but i like it for magic and resonance, especially for games where longevity might not be great.