I've been using the latter for a couple of years now for my inshore skinny redfish hunts.  It's been a great no-drama caster, even in my high wind environment.  I even mount this on one of my 10'6" surf rods to sling 1.5oz sting silvers and it casts them a country mile. 

 

I've been thinking about picking up a new one, but see this Zillion HD.  Is this a more durable/"better" version of the Coastal 200, or is the Coastal still a better reel for what I want to do with it?  They both seem to have similar builds and specs, but if the Zillion is a little more durable from a build perspective, I'd be interested in giving this a shot.

 

 

I have the TW HD, but haven't had the 200 coastal. 

I would imagine they would be pretty comparable, but I haven't taken apart the coastal to know. 

I also don't fish salt, because I dont live near it. So take my opinion with a grain of salt. (Pun intended)

TW HD has an aluminum frame and handle side plate, brass gearing.

Tw HD also has magsealing, so salt water should be fine. 

 

If you're happy with the coastal, why not go that route. It's cheaper anyway and if it's working for you.