I'm sure you already know this, but I have to say it... Common sense will tell you that an SMPL clone that DOES have a solid one-piece build is every bit as good as the authentic that costs 5x more. Milling a hole into a chunk of copper bar stock is not cutting edge technology. This is basic machine shop stuff that can be made on the cheap, so you should buy it on the cheap. Save your bucks for
real technology.
I'm not aware of a single manufacturer that is making them out of a single piece, I have an extremely convincing clone next to me that I can assure you does not perform as good as my authentic and though it looks to be, is actually not a single piece tube. I purchased multiple clones to check out the design versus the authentic because I wanted to have a complete beater mod that I didn't care about pocketing/scratching but my deductions were correct that all of them thus far appear to be using two different designs of press-fit top caps. I own the clone you've got pictured in your avatar, from your pictures in the authentic SMPL thread on page 18 you can actually see that it appears to be the press fit cap that has been cleverly hidden with some grinding/machining up top. Several users have already had this press-fit piece pop out and I personally believe that piece along with the switch tolerances is the reason the clone has .34V higher voltage drop than my authentic.
Is the SMPL clone good? Yes, it's actually quite good
for a clone. Does it stack up against the authentic? Not even close.
I'm not preaching here, I own a dozen clones of all kinds of various mods. Hell my Kepler Stingray X clone is actually better than the authentic with less voltage drop! Performance is the ultimate deciding factor for me and I'll assure you that if you put any of the current SMPL clones up against the authentic there will be a decided winner and it will not be the clone.
Edit: I wanted to show some pictures that I wasn't able to find online, here is a comparison of the SMPL Authentic Copper and Clone. After I compared them I took the liberty of proving the press-fit top section, even though it does not look NOR act like it is. All I did was take a 1/2" drill bit flipped upside down inside the tube, two moderate taps onto my desktop and the press fit 510 section popped right out.
Sure looks like one piece, but there is a teeny seam they tried to hide. Evidence below, clone is on the left in both sections of this picture. I was told when I purchased this from the manufacturer that it was a single piece tube, I specifically asked this question beforehand.
This was NOT hard to pop out and was already tarnishing between the pressed connection, hello voltage drop! Again, clone is on the left.
Clone is on the RIGHT in this top section, Image editing before 9AM doesn't go well. Press-fit FTL.
It's not exactly cheap or cost effective to mill out 70mm of an entire blank of solid copper round stock, the tooling costs money and will wear down pretty quickly doing it over and over not to mention the cost of the material! However, it is much cheaper to buy the appropriate size copper tube stock and do minimal machining with a pressed in 510 section.