Question Diono Ranier or Britax Advocate ClickTight for small child?

My son is 5 months old, we're in Canada. He is a small baby, in the 25th percentile for height and weight. My husband and I were both small kids (short and very skinny) so I don't expect him to be huge. We're looking into getting him a convertible car seat for a few reasons. We don't really carry his infant seat around anymore, I find it hard to get him in and out of it (Graco 35) and he hates the car and some people have mentioned that changes when they go into the convertible.

We are stuck between the Diono Rainer and Britax Advocate ClickTight. The prices are almost the same so that isn't a factor. I can't go look at the in person because I'm in the middle of nowhere.

-We drive a Ford Escape (SUV)
-I want the car seat to be in the centre seat (our car allows centre latch)
-I'd really like to be able to see him through the mirror still but don't think that will be possible because of the height
-My son has been sitting unsupported since 4 months
-My son gets hot fairly easily
-I want to RF as long as possible
-We aren't planning more kids so we only need 1 seat in the row

I like the Diono because it has higher weight limits, but I've read the booster is useless.

I like the Britax because the ease of installation, the clicking straps would make it easier for husband and grandparents, its higher so he could see out the window and the 7 recline settings.

Really for a short kid the world (of car seats) is wide open for ERF! You probably will not need the extra height/weight of the Ranier/Advocate. But if those are the seats you want, go for it! I will say I've heard for a sweaty kid the open sides of the Radian are better for allowing air flow. Most kids outgrow the car seat by height vs weight so the extra weight of the Ranier vs the Radian really wont help you. Yes the Diono booster is useless, but the Britax doesn't include a booster function so I wouldn't consider that a fact to be in favor of one or the other.