Around 10 years ago, a friend gave me a Nagoya NA-771 2m/70cm antenna to suit hand held radios for the purpose of testing it. He had bought two of them on eBay for around $10 each.
These are often sold without specifications, but where specifications are given, VSWR is given as 1.5, though not stated as maximum so should perhaps be read as typical.
This article looks at 2m performance alone.
2008 purchase
Above is a VSWR sweep around the 2m band.
VSWR at 146MHz if more than specification, but less than 2.0 below 147MHz.
2016 purchase
Above is a VSWR sweep around the 2m band.
VSWR at 146MHz if way more than specification, but less than 3.5 over the whole 2m band.
The purchase price was refunded due to failure to meet specification.
2019 purchase
Two antennas were purchased for $24 incl post.
Above is a VSWR sweep around the 2m band. Two antenna were tested with almost identical results.
VSWR at 146MHz if way more than specification, but less than 3.5 over the whole 2m band.
These antennas did show VSWR minimum around 1.5 at 165+MHz.
The purchase price was refunded due to failure to meet specification.
Above is a section through the loading coil unit. The centre conductor of the coax connector is connected to a steel spring (weakly magnetic, so probably austenitic stainless steel), then to the antenna element (which is 8 weakly magnetic wires wound in a helix).
Conclusions
The three antenna vintages tested above had different shaped coil enclosures and different markings, all claimed to be Nagoya genuine product by Revex of Taiwan.
Purchasing the Nagoya NA-771 on eBay is high risk, experience is that recently listed products are unlikely to meed specification at 2m and that is reason enough to reject them.
The antennas can be purchased for as little at $3 each incl post, and there appears to be three kinds of packaging in item descriptions. They are probably all dysfunctional fake copies and worthless cheap Chines junk.