Never tried those but can safely say, "You get what you pay for" If sound quality is not critical, then knock yourself out. I see nothing but headaches in your future but at least they are cheap headaches
The Sennheisers (assuming you are talking about the G2) are not Jurassic Park level wireless but in fact what is considered the very bottom of the line acceptable wireless for non-theatrical video projects. Wireless that go below that are in the "Radio Shack" realm and general do what they are suppose to in the sense you couldn't sue the manufacturers for fraudulent advertising. Beyond that don't expect much and you will be fine.
that was the same mic set-up i bought first. i upgraded quickly! i like azden and went to the Azden 100LT. it works alot better and gets better range. the main problem i had with the WLX-Pro is that is has a constant low static and doesnt take much to get alot of static from many items in between the reciever and the transmitter. if you really want a WLX-Pro i'll sell you mine 100 shipped. here is a link to BH 100LT setup http://www.bhphotovideo.com/bnh/controller/home?O=productlist&A=details&Q=&sku=287689&is=REG&addedTroughType=search