On the one hand, it's great to see that developers are taking an interest without, apparently, having any direct association with the community.

On the other hand, the amount of scaremongering drivel flexispy spout on their website about why you desperately need their software, borders on farcical.
The particularly entertaining "information" is:

http://flexispy.com/cheating-wife.htm
http://flexispy.com/cheating-husband.htm

Also, from a purely technical side, this software seems to function by uploading sms's, call logs, etc to flexispy's systems. Not only does that make the software illegal to install onto any device other than your own throughout the EU at least (for data protection reasons, even if nothing else) but the target would have to be a ***** to not notice all the data usage/charges shortly after making/receiving any phone calls.