Currently it feels very clunky. I understand for the weapons that have their selector switch no where near the thumb (which are rare) but most of these weapons are fairly quick to switch. In game its currently a whole function like priming a grenade. It doesn't have to be instant but right now feels like the person handling the weapon has never handled one before.
It doesn't always register on the first click it seems. Might be contributing to that feeling. I think I commented on the subreddit that leaving the firemode HUD element up all the time would help with this, because sometimes I'll try to switch while focusing on other stuff and there's no feedback to be sure it happened unless you see the UI change.