Viral tell a friend 2.0

There seem to have 2 good 1 which is.

viralinviter . com or trafficxplode. com

here is my question guys, would appreciate it if u help me out.

1.Anyone have any suggestion which one is better or more reliable?
2.where do you usually put the viral inviter feature as in during sign up or after sign up completely or other for maximum impact?
3. is there other out they which is far cheaper? (can't afford the price due to currency factor, perhaps anyone have the script can contract me for further discussion. ^^

Thanks a lot..

P/S: not sure is the correct place to ask this question or not.

http://www.expertzzz.com/Downloadz/view/3252 (50 $)

but i like it free-- http://openinviter.com/ -enjoy!