We really enjoyed our stay at Shunsukes place. The ride there from Narita was quite easy (we chose a rather cheap (998¥) ride that took about 1h). To us it was a little difficult to follow the instructions of how to get to the place from Machiya station. I will add below how we decided to walk. I've told Shunsuke as well, maybe he'll adjust the description. (*)
Machiya is a rather small and quiet place, very pleasant. However if you look clearly foreign, be prepared to get a few looks. It's not disturbing though! Going back to Harajuku/Shinjuku etc took us about 30 minutes from the station (Chiyoda line to Nishi-Nippori and then Yamanote line)
The house itself was much smaller than expected. It was completely enough for the two of us, but I don't think we would have felt comfortable with a third person, albeit a futon in the closet suggesting that people are allowed to stay there with 3 people. It was super clean, we had everything we need. The only thing we bought was a new sponge.
The pocket WiFi was a great help and don't worry. It doesn't run out of battery or data volume as fast as you might think. It served us well the whole day!
The self check-in was super easy, both, retrieving the key as well as the actual check in. Though I might add: as women we weren't happy to have to take a selfie after a 13-14 hour trip with almost no sleep and makeup ;) But I think that was the biggest "flaw". We really enjoyed our time at this place and would certainly visit again!
(*) Walk from Machiya Station (the Exit Shunsuke suggests) up until the second 7eleven (ca 7-10 min walk) and then turn left. Keep walking straight. You will pass a side street with a pharmacy and a supermarket (for orientation). At the T junction turn right and immediately left. Beware, it's easy to oversee at first glance. / Alternative (Our preferred route): Walk from the station up to the little junction of Main Street and a little side street on the left that is marked with a game arcade with a colourful/rainbow coloured logo. From there you can see the second 7-eleven though. If you walk up that street you will pass a washing salon (on your left), a supermarket (on your right) and you'll end up at the crossing where I've mentioned the pharmacy and supermarket earlier. So turn left there. At the T junction turn right and then immediately left. From then on just take a look at Shunsuke's pictures, you'll easily recognise the right house (on the left side).