If i remember from the old Clarence Lee articles the singles ran well but were not powerful; so the pattern people were not interested,which ruled the day. When Robertson got the company, he wrote Lee saying he had spares but no new engines would be made; I guess when no one wanted spares he put the others together. I think he was hoping to protect his multi cylinder collection value when he bought the company. I also remember a twin was used in a Pober Pixie in Model Aviation by Wisher and he noted that the twin looked cool in the cowl but had the power of a .40 single.