HTC will fix the screen either way, the warranty question just determines whether they charge you or not. I think the charge is $250 if the warranty is not honored. So not much more than your local shop is going to charge. Plus, I think taking the phone apart is tricky, so I'd probably trust HTC to do it more than a local vendor. I've seen some real hack jobs on the One X (which is polycarbonate not metal, but similarly difficult to disassemble) by random repair shops. Although of course the quality of workmanship by repair shops will vary, and I'm sure there are plenty of good ones out there.
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Phone: AT&T HTC One (M8)
Tablet: Samsung Galaxy Tab Pro 8.4 (WiFi only)