I guess I have too many ideas and inputs to be a spk parent so cannot give you first-hand experience concerning your question. (Apology to my daughters)
Having said that, I am quite sure children in spk should be very happy since this is how they design the kindergarten program there. I have asked my friend concerning this just to make sure and below are the comments:
"Teachers are demanding but children have a happy kindergarten life, the kids there are happy with the lessons"
"Teachers put efforts on politeness and discipline"
At the end, children should enjoy happy life in any kindergartens unless they are unfortunate to find bad teachers. The teachers there in SPK are very stable with low turnover so I think they can keep the quality of the standard very high. Whether kids will enjoy their pre-school years are often affected by how demanding the parents are and what do they expect.