Electro-stim machine recommendations?

Hello.  I am looking for a decent, yet affordable unit for my practice.  Additionally, I have a patient that needs to use tens stim at home.  Can you use a normal electro-stim machine for Tens with different leads and pads?  Is there anything special that I need to look out for when converting electro-stim to tens? 

Thank you for any recommendations and advice that you have.  I am not very knowledgeable about these products and it's difficult to glean anything substantial from the catalogs.  What do I need to look for in an electro-stim machine/tens? 

Thank you, Lupin, L.Ac, RN

p.s. I'm so glad I found this site! looking forward to participating.