Product review (1 stars): There is no reason anybody should need this adaptor.
There seems to be so much confusion and misleading reviews about this adaptor and the different mounting systems.  If you purchase one of the the Waste King EZ Mount disposers, a new mounting kit is supplied in the box.  Yes, you can try to save time by paying $10 for this adaptor kit, but why?

First, most disposers are available with both mounting systems.  I purchased the Waste King L-8000 which uses an EZ Mount, but I could have just as easily purchased the L-9980.  The latter is basically the same 1.0-horsepower unit but with a 3-bolt system. Understandably, this doesn't help if you've already made your purchase and were unaware of the difference, but it's still not going to save time by using the kit with your existing 3-bolt mount. If you have not purchased a disposer yet, purchasing this adaptor with an EZ Mount doesn't make much sense at all.

Installation - It most cases is it NOT easier to install the EZ Mount with a kit.  The discharge/output port is a standard height on most brand disposers.  That means the new unit should line up perfectly with your existing pipes, unless you use an adaptor.  The adaptor will lower the unit. You may be able to tilt the pipes down to line up, but it most cases you will need to purchase new pipes (and a hacksaw if you don't have one).  I cannot see any circumstance where this would be easier than replacing the old 3-bolt and flange.  Removing the old 3-bolt is not hard, I cannot emphasize this enough.  You take a screwdriver and loosen the three bolts.  There is a clamp ring at the base of the flange that can be easily popped off with a flathead screwdriver or pliers.  Once the clamp ring is removed, gravity will remove the assembly and the flange can be pulled right out of the sink.  Even with hardened plumbers putty, it will pull right out. No problem. That's it!  After that the EZ mount will install literally in about 5 minutes or less.  If you have to re-align your pipes there is absoutely no way you are going to save time or money.

The only circumstance where I can see people needing this adaptor is if they unknowingly purcheased an EZ Mount disposer over a similar model with a 3-bolt...and are either 1. picky about how the flange looks in the sink, or 2) do not like the slightly smaller diameter splash guard.  In the case of the flange, you can still order specialty flanges in different colors and looks, but at a cost.  To keep your original flange you would need the kit.  But again, that is only if one unknowningly purchased an EZ Mount when a similar 3-bolt is available, and your objection is the look or style of the flange or splash guard, NOT functionality.  Otherwise there is virtually no circumstance where you need this adaptor, or can use it to save time regardless of which disposer your purchased.

My advice, just pick a disposer with the mounting system you prefer.  For me it doesn't matter because I would always prefer to replace the old mounting system with the new one in the box.