I think it's safe to assume the SlantPro will get the job done faster, and likely a bit more accurately - is it massively more rigid, and more accurate than "mill-turning". Plus setup would be a bit faster. But, if you're not in a huge hurry, the parts are small, and you don't require extreme accuracy, the RapidTurn should do the job just fine for far lower cost.
One more suggestion: Take a look at mfg.com. It's a free website where you post your drawings or models, quantities and schedule, and within a few days you'll have multiple quotes from shops around the world to make the parts. I've had really good luck getting parts made there, even in small quantities. The most surprising this is, in several cases the price, including shipping, was less than my cost for the raw material alone. It costs nothing to post your design and see what response you get, and you might get a pleasant surprise.
Regards,
Ray L.