Any time you move to a new product source some things are going to be different. Unless you are being squeezed at the margins I'd probably stick with TeeSpring especially given your apparent favorable opinion of your experience with them. Said another way ... if it ain't broke, don't fix it?
Is it broke, or are you simply getting spoiled and a bit greedy? If it's broke, it's definitely an option to go with the cheaper supplier as long as your reputation doesn't suffer, and you are comfortable with the possible risks of customer dissatisfaction.
It's also possible TeeSpring got to the party first, has most of the market, and can trash talk whoever they want on scale to minimize people pinching their margins, so maybe go with your gut ... or consider small tests to find out how you like the cheaper guys stuff.