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Sugata
The Japanese Wikipedia places him among the Edo swordsmiths of the Kanbun-era shape (寛文新刀, Kanbun shintō): blades with little curvature, a short point and a stiff look, like those of the third Yasutsugu, Izumi no Kami Kaneshige, Hōjōji Masahiro and, above all, Nagasone Kotetsu. The wakizashi of the Tokyo National Museum, 40 cm long with 0.7 cm of curvature, is wide and has a large point (大切先, ō-kissaki); the museum notes that there are similar cases in Kaneshige and in Kotetsu, and that the blade therefore has great documentary value.
Hamon
The wakizashi of the Tokyo National Museum has an undulating temper (湾れ, notare). The Japanese Wikipedia says that his manner resembles that of Kotetsu.
Nakago and mei
His signatures are 大和守安定 (Yamato no Kami Yasusada), 武蔵國住大和守安定 (Musashi no Kuni jū Yamato no Kami Yasusada), 富田大和守安定 (Tomita Yamato no Kami Yasusada) and 大和守源安定 (Yamato no Kami Minamoto no Yasusada). What stands out most on his tangs are the cutting-test inscriptions (截断銘, saidan-mei), which he has in abundance.
Who he is confused with
Because of the shape and the resemblance noted by the Japanese Wikipedia and the Tokyo National Museum, the first name he is compared with is Nagasone Kotetsu, and then Izumi no Kami Kaneshige. The signature and the cutting tests on the tang are what set him apart from them.