The Radians install just fine in the second row of a Sienna. It's the 3rd row that causes issues. It fits fine RF in both outboard positions. I didn't try it RF in the middle of the 3rd row. But FF is a problem. The rigid buckle stalks in the passenger side and the middle of the 3rd row make for an impossible install. I got it fairly tight on the passenger side, but there was a lot more than an inch of movement front to back. Middle was impossible to get tight. One side of the seatbelt is a rigid buckle stalk while the other side is a LONG buckle stalk and even with it twisted 3 times I couldn't get even close to a tight install.
It does install just fine with LATCH in those positions, though, but because of the placement of the LATCH, it makes a 3-across situation difficult when installed with LATCH.
It installs beautifully FF w/the seatbelt in the driver's side on the 3rd row, but of course, that's the ONE spot without a tether anchor. :thumbsdown:
These are the issues the Christineka was referring to in regards to the Sienna.