Several years ago I bought a HF, opened the box, and took it back. Then bought a 'twin' from dabay. It worked.
Then Titanium came out, went on sale, and I could not resist. Have a pile of parts to make the twin "DCEN" but have not done so.
Using the Titanium, it seems to weld for a spot...
One thought on the Titanium series to consider is that their duty cycle seems to be very under-rated. I've seen some use them for a lot longer than you'd think they would run without a break.
tom