Usually a chain and rear sprocket will last the life of two front sprockets as the front sprocket wears much faster.
The advice is to fit a new split link when fitting the second front sprocket as the spring clip wears and can get thin increasing the chance of it popping off.
You will find one on most dirt bikes and even some low cc race bikes etc.
It certainly makes it a whole lot easier to replace a run of your chain on the trail if a split link is in use. You just take some long nose pliers with you and you can take the clip off. Some people call them a clip link.
If you dont know, there is also a correct way of fitting the split link, when the link is on the top run, the closed end of the clip must be facing the engine.
Good old DT's - on the tracks I've been out on again I find that alot of the time I'm riding in the rut by the bushes. When i used the TTR i just felt that bit uncomfortable riding it there.
On the open stuff where you have space the TTR is very good.