We ALL trust Kurt! Did he know you were gonna freeze 'em?
The dropper rubber bulb can deteriorate or possibly crack after freezing. The plastic inner cone caps are the more secure/stable option.
Send Kurt a PM to verify my suggestions. If he says otherwise, PLEASE let me know!
Iffy, the bottles listed here are with eurodropper inserts, and regular cap. They are not the rubber bulb dropper cap. These are the ones I use, and have for years with excellent results.
Here is the amber 30 mL bottle:
Amber Euro Glass Bottle 30 ml w/ Dropper Cap (Blk)
It is called a dropper cap I think because it is able to fit the mouth while the eurodropper insert is in place. The cone capped bottles are fine for freezer too, but then you don't get the benefits of the eurodropper insert (no spill, syringe access, and if you want you can take them out). The combo of the cap and the insert will create a gasket seal like the cone caps will. In fact I think the euro insert is the same polyethylene that the cone is.
I have also found these euro inserts and their caps fit TFA 15 mL bottles. Good for often-used flavors to keep them from spilling if you knock it over...and I have before. I wish I could just buy the euro inserts and their caps, so I can spectum-up all of my TFA bottles.
BTW, thanks for the vote of confidence!