First let me say congrats on your nice Bear! Of course I still don' t think it' s fair you getting all that hunting in so early As for the thunderheads and UBAR' s. In my testing the only time it matterd was when shooting the thunderheads into a hard object on a carbon arrow. The O-ring would get crushed making the blades loose and subject to fall out. By using the UBAR' s it makes a more secure fit and this helps the head retain the blades. For deer size critters you may never see a differnce as far as preformance on game goes, but for large animals like you hunt I would not consider using thunderheads on carbons without the UBAR' s. If you notice now NAP is now selling " thunderheads for carbon" packs with the UBAR' s included, their is a reason for this. I think you will find the thunders to be excellent in every way, sharper than your Muzzys, but not as easy to work with.