Mikhail A, welcome to the forums!
I have done both the Otter and the Olifants River Backpack Trail (ORBT) (as well as others, like the Fish River Canyon).
The biggest difference for me is how easy the walking is compared to other trails. On the ORBT, there were one or two very small uphills when we took shortcuts across river meanders, but besides that it was almost flat. The paths are also mainly sandy and very easy to walk on. What a difference it makes not having to look at the path all the time so that you don't catch a rock or a tree root. Almost all other trails, Otter included, have a fair amount of elevation gain and loss.
The backpack trails are wilderness trails in that there is no infrastructure at all, so you have to carry everything, including tent. Hutted trails like the Otter are obviously very different. Wilderness trails like those in the Drakensberg also require you to carry a tent etc.
From a logistics point of view, I think you will have difficulty with a Kruger trail. It is not easy at all to get to the departure camps without your own car. The Otter is a lot easier, you can fly in to George or PE, and there are lots of shuttle companies and also small accommodation places that will shuttle you.
Please let me know if you have any more questions.
Also, please keep us updated as to your plans, if you need someone to join you on your trail I'd definitely be keen!
The 'mite formerly known as joshilewis
FGASA Level 1 GuideGlen Reenen TR
15-18 June: Berg-en-dal