I've not been on a Sea Finn boat myself, though my neighbor at the winter dock
is a 41*. Below information is mostly from Finnish web discussions.
Many of the earlier boats were owner completed, but there are yard finished yachts also. Earlier models have glass hull
and wooden superstructure, but later models are full glass, with optional teak
decks. For the serial
boats the designer
is different from Siltala (Nauticat) yachts, but apparently there are some persons from Siltala who joined Sea Finn. They do share many design principles.
Build quality should be excellent, also the interior
woodwork on yard finished yachts.
Most popular model was the 39 with canoe stern which looks a lot like a Nauticat. The 41 and 411 models have a vertical transom. Some yachts have a added swim platform/extra length. There are other models, but little information available.
One example of more recent one-off yachts by the yard is s/y Anya, which is often docked in the center of Turku. A stunning boat: . : S/Y Anya : .
Sorry can't be of more help.