I have owned the Five Ten SAR shoe for about a year now and I have taken them down approximately 15 canyons. These shoes are absolutely essential for technical canyoneering because of the stealth rubber soles which have unbelievable grip in both dry and wet conditions. Whether rigging a rap station or downclimbing, these shoes provide stability in precarious situations.
I have used both the SAR and the Canyoneer 2 and many folks are unclear with respect to the differences. The SAR has a steel toe which is both good and bad. On the con side, the steel toe adds weight and does not allow you to jam your toe in smaller spaces while stemming or climbing. On the plus side, the steel toe has saved me bruises numerous times on falls or when walking in rivers with limited visibility below. The rubber and grip is effectively the same between the two models.
I typically wear a size 10.5 or 11 shoe and I went with the 11 in the SARs. I have wide feet and the 11s provided me with a bit more room on that front when I wear my 3mm neoprene socks with a merino sock underneath. Five mm neo socks would be a tight fit, but that is more about the width of my foot as opposed to toe room.