@MC-509 thanks for asking this as I am attempting to figure this out too.

  @MC-509 There is a very important difference in terms of warranty.  Be careful with a purchase of the EP25. 

I bought a box of four of the EP25s along with some other KASA units.  I will say I REALLY like the technology.  We have automated our outside Christmas lights and various appliances throughout the house.  

 However, one of the EP25s failed, and support is giving me the runaround regarding replacing it.  They are stating they are unable to replace individual EP25s and are requiring that I send four units back (one failed and three working ones).

So, to get them to honor their warranty, I would need to remove three working units from my app and home, ship them all four units back, lose the functionality while I await replacements, then go through the setup process again.  This would cost more than an individual unit for shipping and disrupt the household.  It's an incredibly bad user experience.  I was planning on upgrading my entire household plugs and light switches, but I have second thoughts based on this.  Maybe the issue is specific to the EP25s, but could you imagine having to ship back multiple light switches if the same happened!

Something to consider when comparing the two and I would consider it an important difference.  Either get an individual KP125, or buy the EP25s knowing that their warranty might not be honored if something goes wrong. 

  @kasauser1234 

Isn't the EP25 compatible with Apple Homekit and the other one not? 

  @Anael Both say they are compatible:

https://www.kasasmart.com/us/products/smart-plugs/kasa-smart-plug-slim-energy-monitoring-kp125

https://www.tp-link.com/us/smart-home/new-release/ep25p4/