Those tapes aren't any good.

There's a lot of people claiming to teach Praying Mantis kung fu, but sadly there's not a lot of people who are actually teaching Praying Mantis.

For some reason, we have about as many Charlatans and posers as Tai Chi.

Real mantis looks like this:

http://www.wle.com//products/VUMANT01.html

and:

http://www.wahlum.com/kung-fu_store.htm
Living Legends of Kung Fu, with Grandmasters Pui Chan and Brendan Lai

Watch Brendan apply 7* on this tape and see if it lacks power.

It's difficult to find real 7* teachers in the world, let alone in the US.