Closet Flange question

I am retiling the floor in my bathroom. The closet flange is mounted direct to the plywood with no gap and no room to lift it up. Once the thinset is applied, the tile will be at least flush or a tad higher than the flange. Do I need to use a closet flange extension to get it above the tile? Is it acceptable to just use two wax rings? What s the proper method for this application?
Thanks.

The 'correct' thing to do is remove it, then reinstall it on top of the new floor. But, many people live for a long time without problems. It's better to use a flange extender rather than two wax rings.

Recently bought one of theseto fix a problem with the flange being too far below the floor - just about 1/3 of an inch or so... but I don't want to have to do this job again... has anyone used these before?

I want to be able to just remove the screws from the existing flange - pop this thing in (it came with about 3 or 4" extension on it already) and then screw it down.

It looks to me like:
a. you have to really trust that little rubber gasket at the bottom of the extension
and
b.is it ok to reduce the diameter of your line to 3" like that? I know it's not optimal but you can get by doing this right?