I have a very similar scenario as yours. My daughter was in CKY p1. I also have a little kid in kindergarten stage. Hope the following sharings would help.
1. CKY kids do have homeworks though the volume is comparatively smaller. Most of them are readings. I don't see her being laid back as her interest in reading was so strong after joining CKY that she read a lot during her free time.
2. If you really encounter any financial difficulties after joining, you may try applying for school financial assistance. Afterall, Po Leung Kuk is a charitable association. If you opt for switching back to mainstream schools, I reckon there would not be any problem academically. However, it may take a while for him to adapt himself as the way of teaching, school environment, and culture are all different.
3. I also have your dilemma. However, I would plan to send my younger kid to other activity-based DSS if not CKY (though CKY is still my first choice), perhaps, at the expenses of not going out for overseas vacation or eating out... I think kid's education comes before other entertainment or enjoyment. Besides, you can save your money for any other tutorial class after joining because the CKY Principal discourages it so much and I don't see the need as well.