I feel compelled to chime in, offer up my opinion, and relate some of my limited experience.
I've run gas checks in 30 cal, 38-55, 7x57, and 416 RM for rifle. In hip-guns, 44, and 38/357. My Hi-Tek coated experience has been with 38/357 Mag. I've just ordered another 2000. I used around 3000 last year, loaded in 38 Spl brass for my '66 and in 357 mag brass for my hip-guns.
A gas check will usually make a bad combination work, IOW, if leading and accuracy are plaguing your combo, a gas check seems to "cure" the problem. They (gas checks) have the advantage of being better grabbers of the rifling. Bullet size and hardness are less of a factor. If new to casting, it's probably less frustrating to start with a gas checked design until you get the feel of lead.
Coated bullets are also very forgiving, but I don't think they are capable of the same velocity as a gas checked bullet, IMO. I however think that if you have a decent plain bullet combination, a coating like Hi-Tek should improve the performance.
With coated bullets "bump-up" or "obturation" seem less of a factor to good performance. I don't know about powder coating as I've only used commercial Hi-Tek coated bullets. The coating is a barrier to gas cutting, doesn't eliminate it, but it certainly reduces it. In my revolvers I see some buildup in the forcing cones, but it appears to be burnt paint, not lead. It cleans up easily. The bore is usually shiny, perhaps a bit of coloration from the coating, but it just wipes out.
I like that my ammo will work in all my guns. I have 4 hip guns in 357, (a pair and a spare), and the throats and grooves are definitely not matched, or ideal. Leading of the throats is not an issue, even though one has 0.360+" throats. 0.358" coated bullets work. I've also used 0.357" dia 358156 gas checked with good results, unfortunately gas checks are not allowed for Cowboy.
The coated bullet I use does not have any lube grooves, a definite advantage when it comes to grabbing the rifling, without any undue skidding. The last thing you want is for skidding to compromise the gas seal, leading on the edge of the rifling is a bear to remove. They don't have a crimp groove either, so I just crimp them into the lead, and don't seem to have any issues.
I've bought a bottle of cheap powder coating and intend on making my own, hopefully soon.