It is well built - all metal construction. Packs very flat which makes the product very portable. Stands on its own, so technically you can leave your phone on the mount and then use it as a stand (unconventional - but it works).
Love the screw down method to keep the phone in place. Far more secure and less cumbersome than the 'elastic/spring action' models. The screw method also allows for larger phones too, even with a case. I am using an LG V20 with a case and there is plenty to spare in terms of phone size capability.
A thing to note: when adding the Boya MM1 microphone, the 'cog' that you spin to screw/lock the mic to the cold shoe does get a little cramped as the screw of the ST-03 does get very close to it.