In my opinion, this is one of the finest stamp sets from the Kingdom of Laos. It was designed by the painter and artist Chamnane Prisayane and engraved by Jean Pheulpin, who received the first prize for best French philatelic art in 1958 for this set.
The set is not rare and is frequently offered for sale online. Its Michel catalogue value is around 20 euros in excellent condition. Your set appears to be complete, but I can't assess its condition since the stamps are inside glassine envelopes.
