Based on some of the other posts such as
http://www.team-bhp.com/forum/street...tml#post708240 (Kerala Roads - Unimaginably Pitiable condition) even the thoppur-mettur-bhavani road appears to be also in a bad state.
The way I see it, it is safer to stick to the big highway. If there is no civil engineering projects then the road will be enough room for everyone. On the other hand, if there is some kind of road work going on, there will be only room for one vehicle to go. Both sounds safer than going on the smaller roads.