I don't have experience in Thanda but I suspect you will get very good value for the upmarket accom and facilities. In Sabi Sand reserve you are paying for the lodge facilities, soft and hard product, but also the 'branding' that comes with Sabi Sand reserve. Thanda is a reasonably large reserve whereas Sabi Sand is unfenced from Kruger NP but each lodge will have a traversing area that they can drive on. So what you see is always some luck.
I am not sure what your comment about scheduled flights is trying to ask. For Thanda there are scheduled flights + a ground transfer (from Richards Bay about 1 hr on sealed highway). For Sabi Sand lodges you can take the scheduled flights to Skukuza or Hoedspruit plus a ground transfer, depending on the lodge it can be a short transit in an open game vehicle or an hour on gravel roads to your lodge. Or you can pay for a 'bush flight' to a lodge airstrip, which is convenient but expensive and limits your luggage capacity (if you are a photographer for instance sometimes a ground transfer is better). Don't discount other lodges / reserves. It really depends on where you are coming from / to, your budget and time, and how much you weight accommodation and facilities/food standards against the wildlife sightings side of things. Oh and the age of your children.