Power foci are the most potent and treasured of all. Possession of a power focus feeds a magician’s Magic directly, making her efforts more powerful in all forms of magical ability. A power focus adds its Force to all tests in which the magician’s Magic is included. A single power focus can increase a magician’s ability to cast spells, call on and control spirits, and bypass astral barriers. A power focus does not help in Counterspelling a hostile spell as it is cast, nor can it duplicate the unique ability of a weapon focus.
Power foci live up to their name. They are very powerful foci that temporarily increase your effective Magic rating. That means they add to your Sorcery, Conjuring, and Enchanting dice pools, [u]along with any other test where Magic is involved[/u[/size]]. Power foci can take any form, but for some reason, rings and amulets are quite popular.[/i]
No significant change, all it does is state the same in other words.
I changed a line up there (bold, enlarged font)
this is the only line that REALLY gives me a pause... and only because of one thing.
Is the check between magic rating and Spirit force a test? or a limiter?
if it IS a test: then it would indeed add to your magic rating for the purposes of drain and Spirit summoning.....
if it is a Limit, then it would not, and you CHOISE to break it at the moment of summoning, and thus incur a penalty. (the physical drain)
now, lets look at how each ruling changes the game.
IF IT IS A TEST:
For the cost of significant Nuyen, and (relative*) small amount of Karma, you can increase your magic rating in leaps, which effects just about everything a mage does.
The only real limitation is that you have to have the foci on you (it CAN be taken), wards can disable it for a time (if forced through a ward), and a small select few other disabilities...
This really limits the power and scope of Initiation. Since you have to buy initiations separately (buy lvl 1, then lvl 2 then lvl 3... you CAN NOT buy lvl1, then buy lvl 3.). Considering that Initiation has always been the PRIME game mechanic for raising an Awaken's potential, it sounds very circumspect that they would include a mechanic that allows you to vastly jump in power for such a relatively* small costs of Nuyen and Karma.
IF IT IS A LIMITOR
Then, the power foci would not add to your magic rating for the purpose of overcasting. Again, given the cost of the power foci, which is considerable, the addition of dice to any TEST using magic is a huge bonus. but not out of the question when compared to the other bonuses enjoyed with the stacking of equipment by other archtypes.... Save, of course the Karma cost... but this is the LIMITOR of being awakened in of itself.
********
If you look at the mechanics in SR they boil down to basically:
<SKill>+<Attribute> +/- <modifiers> [limit] VS <SKill>+<Attribute> +/- <modifiers> [Limit]
sounds likely that the Power Foci is a modifier to me.