TL;DR - I will not be purchasing anything further from seller "glassdiy". Not a great experience, so do business with them at your own risk.
So seller "glassdiy" doesn't get amazing remarks. I bought three pieces, a Y adapter and two "right angle" 18mm M>F adapters.
Pros:
-Free Shipping
-Relatively fast (1/17 order, 1/30 received)
Cons:
-Both "right angle" pieces are not actually right angles. If I had to guess they're somewhere between 95 degrees and 105 degrees. That sort of loose tolerance will not work for my purposes.
-When I brought this to the seller's attention, they requested photo evidence. DHGate has been very unintuitive trying to figure this stuff out, but I promptly linked several photos for the buyer. They stopped responding at this point.
-After opening a dispute, the seller went with the most bizarre solution. They're refunding me the $9 or so the pieces cost, sending me two new ones, and for some reason requested I ship these two back to them at their own cost. The shipping from my side ALONE was nearly $19, and I only paid about $21 on this order, so I'm pretty sure they are losing out at this point...
Just wanted to provide the conclusion to this saga. It's now been a month and a half, and it's finally "resolved". What I mean by "resolved" is that the seller never replied past the initial agreement, then just stopped responding to DHGate also. After waiting around forever, DHGate just cancelled the order, refunded me my original purchase cost ($21) and apparently is covering my return shipping fees separately ($19).
On one hand I feel a little bad, as this wasn't my intent. I simply wanted the seller to send me the right pieces, not refund me more than what I originally spent. Now they're out the small pieces they sent me and obviously I'm leaving a poor review.
On the other hand...come on now. This was a pretty simple, small transaction. Why are you selling things on here if you can't respond to your customers? While it's not the resolution I wanted (and doesn't make sense financially), I'm sort of glad they're not going to attempt to ship me replacements. I could see this going back and forth multiple times, and at about a half month each way, no thanks.
I've learned my lesson, and will now only be getting adapters like this from OGB.