Experience with Fizik R3 Road shoes?
Updated after a week of use:

I recently purchased the R1 from a local bike shop. Summary:


It's the most comfortable shoe I've worn (which isn't many).
The R1 especially needs a bit of wearing in to reshape the leather and custom Sidas insert to the shape of your specific foot.
The included insert is rather extreme and may be initially painful but quickly reshapes to the shape of your foot after a few hours of use. I tried my own Superfeet inserts but went back to the one that ships with the shoe.
The shoe has several minor adjustments that can be made (tongue padding, straps, insert).
There are several form-fitting features that really grip the foot in a comfortable way (especially the heel).
Subjectively, they perform really well. There's the sensation that all foot movement goes right to the pedals and into pure speed.


Detail:

The local bike shop had the R3 in stock. I tried their largest size (44.5) and they felt about right, so I ordered the R1 in the hope that they would fit the same. I wish they had the 45 to compare, but I went with the 44.5 anyway.

I received the R1 a few days later and they seemed a bit tighter than the R3, especially in length. However, I'm told this is intentional since the R1 is all kangaroo leather and will stretch a bit.

They immediately felt really comfortable for my foot. Bike shoes are hard to review since foot shapes and sizes are different for everyone. The built-in arch support is very tall at first, but quickly changes to fit your specific foot. I didn't use any heat treatment other than just wearing the shoe on a few rides.

I did a 50km ride and felt great, then (possibly unwisely) a 250km ultramarathon (with 3km of vertical over three mountain passes). Other than a preexisting issue with a bone in my right pinky toe, the shoes were extremely comfortable and performed very well. I was very happy to be in this shoe.

Sizing is tricky. The R3 is a bit longer than the R1 since it's not made to stretch at all. The R1 is supposed to stretch a bit in both length and toebox width over the first few weeks of use.

Apparently they run big, maybe even a full size big compared to Sidi. I wear a 45 in Sidi and the 44.5 in Fizik was comfortable for me.

The grip that this shoe has on the heel is incredibly firm without being uncomfortable. I find that I can leave the straps fairly loose and still get good power on the pedals throughout the full stroke.

They were very squeaky at first with my Speedplay pedals, but a bit of Carbon paste between the cleat and shoe eliminated all squeaks.

Overall, I'm very happy with this shoe. I plan to use them for 5-10 years, so the price was well worth it for me. It's probably almost impossible to try the R1 in a store (they won't stock it), but you may be able to find an R3 to try on.