Let's thin the rhetoric out a little:
1.) "If the Amsoil bottle says meets Mazda M-V specs (and it does say that) then the dealer is going to then deny your warranty claim? That's not true." You are wrong and don't understand blatant terms and conditions.
Mazda M-V is a Mazda spec and is not licensed/certified/rubber stamped by the API. It's a set of minimum requirements set by Mazda that the fluid manufacturer has to meet. Mazda does not run a 'certification' for MV like GM does for Dextron so there's no additional testing needed. It's on the Mfr of the fluid to tell the customer where to use the fluid. The same is applicable for Redline, but you seem to have forgotten that.
2.) If you use engine oil that is not API certified in your engine, Mazda will deny your warranty claim if they can prove you used non-certified oil. That's a fact no matter what kind of snake oil Amsoil is selling. Stop telling people otherwise.
Here's what an 06 Mazda6 manual says: "Only use oils 'Certified For Gasoline Engines' by the American Petroleum Institute (API). An oil with this trademark symbol conforms to the current engine and emission system protection standards and fuel economy requirements of the International Lubricant Standardization and Approval Committee (ILSAC), comprised of U.S. and Japanese automobile manufacturers."
Amsoil's XL and OE lines have the logo because they are Group III based oils and their formulation varies very little since they're not meant to be cutting edge oils. As for their signature series, Amsoil refuses to pay the API to certify Signature Series because they do not allow base stock substitutions on 'true' synthetic lubricants. Amsoil doesn't want to be limited to one supplier, as this could potentially disrupt production (they are only about 5% of the market). If they certify their lubricant using one manufacturers base stock, Amsoil would not be able to switch suppliers without re-certifying the lubricant over again. This is very expensive. Amsoil SS line exceeds API SN specs by far, but since the API is biased on petroleum base stocks, it's not a fair game for PAO and Esters. Not on the financial side of the equation.
So feel free to use OE and XL as they ARE API certified, but certifying their Signature Series would back them into a corner. Knowing this, Amsoil decided to do what most other companies don't: offer a warranty if their product actually is at fault.
Here's their warranty info:
http://www.amsoil.com/lit/g2488.pdf and
http://www.amsoil.com/lit/g1363.pdf
If you use engine oil that is not API-certified and your auto manufacturer can prove it, you are screwed.
Read the Amsoil PDFs, it'll clarify a few things for you.
Transmission fluid is not API-certified. You will find that if your transmission fails while using fluid other than what is recommended, you have no legal recourse to argue against Mazda's claim that your fluid was not sufficient in meeting specs. I can make transmission fluid out of canola oil and say it meets specs, yet it doesn't. That's what API is for.
Hold the phone, so if the API isn't involved in transmission fluid, why do you bring it up when talking about it? I'm confused. The OP using Redline would be just as 'bad' as using Amsoil in this case as neither are 'certified' for transmissions. You have no choice but to rely on the mfr's word that they're being truthful.
Here's Amsoil's listing on the API site:
http://eolcs.api.org/companyInformation.aspx?id=226450
Click the logos to view certifications. Certain products were chosen for certification to allow participation in government and fleet bids which *require* certification for submittal.
And can we keep this on transmission fluids since that's the topic of the thread? PM me if you want to discuss this further and I can get you any/all info you may need.