ただし押し込む瞬間気圧の変化のせいでしょうか、耳がツンとするのが難点です。

、。

The only downside is that at the moment you push it in, probably due to the change in air pressure, you get a sharp sting in your ears.

Literal

However push-in moment air-pressure [possessive-の] change [possessive-の] fault [wonder-でしょうか], ear [subject-が] stings [nominalizer-の][subject-が] drawback [copula-です].

ただし 'however, provided that' introduces a caveat. 気圧の変化のせいでしょうか 'probably due to air pressure changes' hedges with でしょうか. ツン is a 擬態語 (state mimetic) for a sharp, stinging sensation — ears popping under pressure. 難点 'drawback, weak point' wraps up the complaint.