I have used both a Tens EMPI Select
http://www.djoglobal.com/products/empi/empi-select
And a IF/IC Empi if3 wave
http://www.djoglobal.com/products/empi/if3-wave
Both have pros and cons in my opinion.
SELECT PRO:
1. Small and only requires two electrodes I use them right above where the "butt crack" meets the spine and about 2 inches to either side. Basically where your natural belt line is.
2. Can run all day if needed and used normal AA batteries.
SELECT CON:
1. Only one setting and uses the "low back" setting.
2. Causes back muscle contractions for me.
IF3 wave PRO:
1. Has a mode specifically for pelvic pain and uses IF IC rather than tens.
2. has a 2 mode approach one that fells like tens and than another pulse throbbing mode that I like much more than the tens.
3. Comes with a pamphlet with two placement options for pelvic pain.
IF3 wave CONS:
1. bi lateral only
2. requires special rechargeable batteries, but comes with 2 of them, a single battery works for 8-10 hours of continuous use for me.
3. Requires 4 leads, and can be a real pain because the lead placement crosses. I found it very hard to try to go out in public and keep the pads in contact.
If I was in terrible pain and I had to choose one I would go with the IF3 wave. But if I had to work and be productive I would go with the select.
Also, I place TAC GEL on the skin at the application site and wait for it to get tacky it help allot with getting the pads to stay on.
I hope this helps.