About Softbank Kaedoki program

I normally change my phone every other year. So, softbank kaedoki program seemed a real deal to me instead of losing half of the money selling my used phone.

But monthly cost of their plan is little expensive. Is it okay if I do change the carrier after 3 months? Is it something negative which may block me to do mnp im the future?

The sales guy said it's okay to change the carrier to Ymobile after 3 months.

Anyone been through this?

by Dangerous_Ring7525