I remember having those rules linked in my Summoning/Binding discussion. I bookmarked them to read at a later time and it never happened (I blame work). I'll have to look them over and see.
My only objection is that it sounds like it basically lets the player run two characters over the course of the game session, which may be a bit unwieldy in larger groups.
No worries, I am currently in finals so I am unable to do all kinds of stuff. We've skipped like 3 game sessions 3 weeks in a row now.
And that is true, though there's ways to reduce problems caused by this, and yeah. It might be a problem for a larger group. My group has a crazy small amount of players so it's not an issue. There's ways to reduce the problem of this, which even my small group is doing. Like my Saber is going by the book on her character type, so she's going to be all honor and such. Where as my character is more of "Dr Doom" honor, I guess that varies depending on the book too, but short answer: not very much. It'll probably come up a few times, will have to see. Though luckily my character has a boss in line with Saber's personality, so they won't be constantly sent out to do stuff she'd refuse to do.
Anyway, there's not a lot of fixes for this kind of thing really, I'd think, if you're worried about bigger groups. Servants are strong and here's my suggestion. Have the PC's all play mundane mortals or weak magic users, then give those mortals a servant that 10 refresh based on those house rules. The mortals wouldn't really be involved in the combat outside of being targets for others.
Second option: Have some players play Masters, and others play the Servants. Odd men out could possibly play both or something or some abnormality like a servant with no master, Archer is a good one for this without something really off the wall, though there is of course many examples of "rule breakers".