You don't really have to trust anyone when using a non-segwit node, I would disagree with that. As a soft fork, segwit doesn't break backwards compatibility. The fact that your node doesn't understand Segwit means that it can't use it, it won't show you the balance of your segwit addresses and it won't be able to send to them. It will just ignore it. Only way you need to trust a Segwit node is if you want to use a segwit address yourself or send to one while running a non-segwit node. It is pretty simple, it is almost like another layer to it from the clear user perspective. What really is happening there is that miners just agreed that they won't confirm certain types of transactions (non-valid segwit transactions), other then that it all seems normal to the old node.