The no lunch at Kew College is certainly a point a few parents have struggled with. It speaks to their heritage as KC started as a y3-Y6 push school where academics and the maths/English exam was all that mattered. They are far from it now although the legacy remains visible with the no hot lunches, no canteen and no outside space and a very regimented day so they can make best use of the outside space available. The new premises to house the two-form year 5 and 6 are good but do not solve the chronic lack of space in the end (Imagine how bad it was before!!) and they chose to have an art space over a canteen but then probably you could not have had a canteen for the whole school as not enough space still (and the house in the middle neighbours would have objected the to and fro between the two buildings)
Depends on your child in the end. KC suits a more compliant and quiet child. Kew Green more mainstream but great facilities and can deal with a wider range of children (including very academic children). Kee Green more expensive than it should be (and will eat any savings from Kee College is you end up there).
Kew College is also less friendly with working parents overall. Watch out KC if you have a happy and active boy too. Everything is more regimented and controlled, 2-3 children leave in every year group at a minimum over the first 3/4 years because they cannot keep up with the academics (check in the Kew College Review magazines when Y6 children joined) and school fills back in years 2-3-4 with carefully chosen local state children. (Speech or running commentary is 'oh no KC don't cull but beware, the pace is really fast so you need to keep up' so you wonder what happens if!) KC entrance rules are not super clear so if you are looking for a place starting Y2/Y3, rules change along the way depending on ? who knows what, but you may never get the chance to an entrance interview, the Registrar making up some poorly rehearsed excuse or backtracking what she said 2 months ago.
The latest year 6 year group at KC was particularly low in numbers, so they lost children and did not replace (I think there were 31 or so out for max 40, which they would have if they can, even when they have a total maximum cap on total children in the school); they had good exam results but not great results or not as good as previous years and a low number of scholarships versus previous years and versus other schools. So all of that speaks for their origins (prep school boot camp from Y3) and how they carefully manage each cohort to get the results they get out of a trimmed and reformatted year group, if you see what I mean. Singapore Maths method and lots of homework, which may or may not suit your child or family. If your child is anything out of normal standard development, then it may not be the best place, as all children are expected to keep up or else. Paradoxically Ofsted/etc doesn't like how they extend gifted children or teach IT (check the reports). That prompted the departure of the IT teacher last year (and Covid ejected this year's new IT teacher) but I think the issues are at the top leadership so a new HM will be a welcome change. Fairly high teacher/TA turnover too due to demands and an ethos that not everybody subscribes to. Extra curricular has improved a lot but at the end of the day, 11+ exams target is what matters (which may be what you are looking for, but beware not to push your child into a secondary school that doesn't suit them long term). Good relationships with Hampton (great actually, they take a few every year) and Kingston Grammar (great majority of Y6 sit for exam but less than half of those accepted end up going) and Ibstock (although this school less so given wider reach to other prep schools and increasing popularity). So overall provides 11+ results but you do wonder if it could have been done in a different way.
So more complex than it seems. I think the change of HM at Kew College will be a good thing, but not announced yet who is coming, they have been trying to recruit for 2 years but failed (I guess trustees not happy with how transition is panning out in the end, and see that culture in the school needs to change) and the so called potential "natural successors" left recently (including deputies and KS2 heads etc) so they have had to go back to square one.
Overall you get some very strong parent support for KC but also those that quietly leave (to Kew Green particularly). If you have a very academic and compliant and quiet child I would not hesitate to choose KC. If you have a boy or a sporty child, or a very smart but free spirit, a musician or want an academic but still balanced education, I would try any of the other 3 prep schools in Kew or travel to Richmond or Chiswick.
So that's it for a bit of detailed feedback, so you are aware of what is coming. Good luck in your choices!