Weighing only 1,000 kg (2,205 lb) the Sai.107 reached a speed of 563 km/h (350 mph) in trials held at the Guidonia research establishment and manoeuvrability proved to be excellent.

Its lightweight wooden construction, combined with a 560 kW (751 hp) Isotta Fraschini Delta R.C.40 inverted-V engine,[2] with a center-line cooling air intake, provided speed and agility.

Flight testing revealed some major shortcomings, most of which were not rectified before the Armistice with the Allies in 1943; the low power and high wing loading resulted in poor climb performance; the light structure prevented more powerful cannon from being used as the recoil forces overstressed the mounting structure; the rear cylinders of the engine overheated during recovery from a dive; the light structure also led to problems, with the second prototype wing exploding during a dive recovery due to internal pressure built up, caused by the lack of internal fairings in the undercarriage bays.

The aircraft entered service in July 1943, flying a number of combat missions against heavy Allied raids over the Italian capital, but without success.

After one month, they were sent to Castiglione del Lago G. Eleuteri airfield (at that time one of the main Regia Aeronautica training airbases and near Ambrosini's factory), where it was planned that 161 and 162nd Squadriglia would take the aircraft into service.