I've never swung thd IDX but I have used two other Whites models. They're very solidly built. I recently purchased the Quest Q40. I don't have much time on it just yet. So far, I like it. It has a very intuitive interface. It's light and has a good collapsible square rod system that does not flex. It collapses quite small for transport. Depth seems good and the audio is great. Choice of one to six tones plus a setting called fesen which when activated let's you hear the iron you're swinging over. It's meant to let you hear good targets in iron infested ground. Overall it is a feature packed machine for the price.
As an aside, Quest is the originator of the cellphone on a handle design as far as I can tell. It's quickly becoming the go to style. They've had some serious legal troubles with patent infringement in the States and therefore hardly sell units here. Which is why they are pulling out of this market. I've read they are popular on the continent. There are several YouTube channels showing them in use in Europe with good finds.
I try not to give advice about purchases so do your research. I can tell you that the Q40 is a good machine.
Good luck with your choice and Happy hunting.
Henry