My advice is not to sweat things. Definitely go easy on the little tike, and let him help guide things no matter how frustrated you are.
We had a portable potty, but barely used it. A adapter on the regular toilet worked at home, and he quickly figured out how to sit ont he edge without an adapter for public restrooms.
Our kiddo had all the mechanics figured out around 2.5 and had been really excited about the cool underwear we bought him, but once the novelty was gone he reverted (normal for him on many subjects). He then went to the underwear for the daytime and a diaper at night. We just went with it, and one day several months he said he wanted to just wear underwear. He wanted company when going #2 for sure. A while later he spontaneously starting standing for #1 (much to my wife's chagrin).
We have had a total of about 4 or 5 total accidents (including nighttime ones) though age 5, don't fret if yours has much more difficulty. Yelling, getting upset, or otherwise making the potty a stressful subject only stands to makes things worse in the long term.
Do bring sticky notes to cover the sensors in public bathrooms. It sucks to stand there with your hand over the thing while the little guy bears down.