I ate here in March (solo diner). I made a reservation at Jiko and when I checked in, asked about availability at the counter, which there was plenty, so they took me there directly. I don't think the restaurant was that busy that night either as even if I got a table I would have been seated immediately.
I really liked eating there and chatting with the chefs. They basically do a lot of the appetizers there, and the chefs do seem to enjoy talking to guests while they are prepping. It was a great way to eat since I didn't even feel like I was having a solo meal!