1) Read their terms and FAQ, or contact them or Allison here. Usually, if it's not mentioned there, it's allowed, but have their confirmation first.
2) They pay for the second page click. No one would pay for blind links for the first (blind link) click.
3) They are trustworthy, if they say no conversion, it is so, and they pay on time every time. Use them! Topcash also has its sister site
http://www.topbucks.com