Translation:When they make a better product I will buy it.
The word order here works like this: [Subordinate clause] ska jag köpa den. The subordinate clause takes up the first place, therefore the verb needs to go right after that.
Compare: it would be the same if you just said:
I morgon ska jag köpa den. – Tomorrow I will buy it.
for me it would be definitely ok, because the meaning would suggest so. However... while tilverkar is only a bit more high/sofisticated; on the other side utvecklar is a bit different for me in the meaning, since it is more to develop (meaning it is not only about production quality, etc, but they have to really do R&D to change the product... so utvecklar is slightly different so in strict aspect I would not accept it as a teacher, but only as an individual speaking with someone...