Hello Dave, and welcome to the friendly Camera Labs forum!
Sad to hear you had bad luck with your super-tele.
But I've come to a similar conclusion in the case of the 1.5x tle-converter I had just bought: Magnifying the images from the original lens (w/o TC) in post-processing just yielded at least as good results as using the TC
So I sent my TC back. See the full story here
Conclusion: It's better to get a sharper and shorter lens than to rely upon long and cheap glass or a TC.
Thomas (beware: Nikon-fanboy and moderator!) My Lens Reviews
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