Long story short, I ordered this unit from two different catalogs, and when I attempted to send one back, the company (CDW.com) would not return it. Now I'm stuck with two. This unit has never been opened. I can tell you from using the other 801K I received, that it is indeed an upgrade from the 701K that I used to use. The AC filtering is a Godsend! Well worth the extra money we paid IMHO. Retail price is $163.75, and the best price I've seen on the net is $142.00 + tax & shipping (though we paid more for it from CDW.com). I am looking to get $120 (shipped). Anyway, here is the text from Progressive Electronic's website: "Our finest wire identification kit, the 801K Premium Tone & Probe Kit offers all the features professionals are looking for. Includes the 77HP/6A High Power Tone Generator with bent nose piercing clips, increased talk battery supply and higher voltage protection, and the 200FP Filter Probe for filtering out AC hum. Tone probe & generator come housed in the rugged woven polyester 700C Dual Carrying Case designed for years of dependable use." I can accept Paypal or money orders as payment. Thanks, and please let me know if you have any questions!