The trip is billed as 'leisurely' - and I'd just say be mindful of the type of people this may attract. If you want to look at India through a coach window, be shepherded around and not have to think for yourself, and complain about not getting biscuits with a cup of tea, you'll be in your element.
If, like me, this is not your thing, use the trip as a means of having your transport and accomodation arranged, then take yourself off on your own, open your ears and eyes and get set to have the most fabulous adventures.
A word about meals: while the group dinner arrangements are handy in places like Munnar and Madurai, there are MUCH more exciting places to eat (for a fraction of the price) - so I'd urge you to get a guide book, look at the local recommendations and venture out. As the trip notes warn, the service in restaurants is painfully slow, so the group dinners actually made for quite a painful frustating experience with 14+ people ordering, fiddling with bills etc.
I'd also suggest that if you want to make the most of your time in Periyar, book extra activities in advance. It's a fair old drive to get there, so it was desperately frustrating to find, on arrival, that all of the extra hikes/safari options (other than the boat) were booked up. We did manage to book ourselves on to an extra day hike and a hight hike too after a lot of fluttering our eyelids, but it was quite a stressful doing so. Skip the stress and book ahead. Oh - and the morning hike arranged with the group isn't much to write home about, so if another activity clashes with the times (like the all day river rafting option, for example) I'd skip the morning walk and get out on the water.
Do explore in Kovalam too - there's a much nicer beach than the main one lined with all the shops past the LightHouse - it looks like it belongs to a hotel, but it doesn't. Get yourself up the lighthouse and you'll see the track leading you down there. A great place for watching the sun go down.
Go to the temples (ladies - take a shawl/scarf for shoulders for all, and you'll need full length trousers or a full length skirt for the Madurai temple - you won't be allowed in otherwise) and take it all in. They're just mesmerising - but you need to spend time there to absorb it; a whistlestop tour won't cut the mustard.
Explore, get off the ubiquitous streets selling tourist tat and let things happen. Yes, be sensible with sanitisation but don't let this put you off having fun discovering new fruits in the markets, sipping coconut water and ordering dishes you've never heard of for the sheer delight of trying something new. Wander, chat, ask and try - it's all there, you just need to let it happen!