These Phoenix tapes are being put together and sold by a member of Tapeheads. And Stranj is right, they are all about the quality of the tape inside. AFAIK, the shell itself is clear and has the metal cutouts at the top. Larry (from Phoenix Tape Co.) had a hard time even finding those... And there are not many left.
The tapes were extensively reviewed at tapeheads.net and were universally considered to be excellent cassettes by those who tried them out. They were put together with a very thick formulation tape stock, so they are limited to C-60 length.
Personally, I would consider these as "too good for use in a boombox" and would only use them in properly tuned high quality component decks. So, if you want a good quality metal tape for high quality master recordings... buy a few, you won't be disappointed.
Otherwise, your only other option is NOS metal-tape lotto via ebay, which also tend to be more expensive.
Frankly, most of the metals I use nowadays were purchased as "gently used" tapes from thrift stores or ebay. I seldom ever crack open a freshy from my tape stash.