Originally Posted by
twospoons
Answer 2 & 3: The number of ovens you buy does not change the number of gems you earn. As with all the coin ovens, you earn gems for each recipe, regardless of whether you cooked that recipe on a single appliance or 18 duplicate appliances.
Answer 1: These 2 ovens are different. The recipes on the Bavarian Oven work as normal, each recipe will give you 2 gems for mastering it, one at the end of level 2 and the other at the end of level 4, as you said. As there are 3 recipes on it, you'll earn 6 gems for mastering everything, so since each one cost 5 gems, you'll end up losing gems if you buy more than one. If you only buy one, eventually you'll have a profit of 1 gem, but it will take you a long time to get there.
The Colonial Oven (it has a little info symbol on it to confirm this) will eventually pay out 12 gems--two after level 2 and another two after level 4, on three recipes each. So if you buy one appliance for 5 gems, you'd eventually have a 7 gem profit. Or you could buy two and still eventually earn a 2-gem profit, but if you get three, you're losing gems.