I also own the Periscope and the X1. I love both of them. I'm still new to the X1 but I feel that I will have a definite purpose for it. I feel like I'll always use the Periscope more, as it locates targets faster, and often I don't even have to bend over very much to locate the target before I ever get the digging tool out. It works exactly as advertised and it is a great product.
There are times when the Periscope is not the tool for the job however. Mainly, it rocky ground, gravel, or ground that is dryed rock hard. Another use is when you have a really deep target that is too difficult to tightly pinpoint. At that time, it is best just to dig a big deep plug, and start scanning with the X1 until you narrow it down.
The main thing for me is not to have to give up on a target. With both probes, I pretty much cover all the possibilities.
It is an expense to be sure, and it ends up being some extra weight to carry around. Until something better comes along though, it is worth it for me.
HH Alton