You are doing just a bit of an "apples to oranges" comparison... the CK20 is a bigger tractor than the BX25. Kioti very wisely, IMHO, decided to offer just a bit larger tractor instead of offering a directly equivalent product to the Kubota. If the Kioti appeals to you because it's bigger, well Kubota also makes slightly larger tractors that you should at least consider. The CK20 seems to fit just in between the BX and the B models in the Kubota lineup. I think all are fairly close in price, so check them all out. Kubota is the more established brand in the US, but Kioti is moving up and makes very good equipment also (Kind of a Toyota vs. Hyundai analogy, I guess).
I always try to suggest new buyers think through the actual work they plan to do in figuring what size and type of equipment to buy. The better you know your work requirement, the more well-considered your buying decision will be. For example, if you have storage and maneuverability limitations at your place, bigger is not always better. And, if you are going to mow your yard with it, a lighter footprint is a good thing. But, if lifting and pulling muscle will be constantly put to the test, you'll appreciate a bigger machine. Most people - but not everyone
- find getting a little more tractor than you think you need is a good idea.