hey...
there r lots of different kinds of putty....tamiya, revell. squadron etc... im guessing that if they sell it at ur lhs it prob ok to use on models.
personally i use squadron green putty, coz i read hear that it can be thinned with DA.
oh, and for ejection pin marks i like top use liquid paper (white out). just try and find a pen dispenser with a fine tip.(i have a pentel correction pen with extras fine tip). the reason for this is that i find its a lot less messier than the standard applicator.
i just remebered, that there are also epoxy putties ( two parts) from what i have read on here (i spend to much time on this site!;)) these are mainly used for scratch building tarps and blankets and such, not really used for filling holes...
hope this helps!