Let me give this a shot.
First, SunPower solar cells are used in most of the solar panels manufactured. SunPower sorts their cells in different classifications based on efficiency and number of defects. SunPower makes their solar panels using different classes of cells based on pricing and also sells their lower quality cells to other manufacturers.
https://us.sunpower.com/products/solar-panels
Other manufacturers have come out with high efficiency solar cells to compete with SunPower. One of those is PERC which is used in the Lensun panels. PERC cells are high efficiency like SunPower cells but with some improvements.
https://news.energysage.com/perc-solar-cells-overview/
SunPower uses both ETFE and PET in their manufacture of solar panels. PET-laminated Flexible Solar Panels generally have lifespans of up to 5 years, ETFE-laminated Flexible Solar Panels have lifespans of up to 10 years or longer. Why aren't all solar panels using ETFE? Cost. ETFE is more expensive than PET and if the manufacturer is counting pennies to keep the panel costs down, it makes a difference.
The backing used for the solar panels makes a difference in the reliability of the panel. Fiberglass gives the best reliability with aluminum and polymer ranking behind. Why aren't all solar panels using fiberglass? Again, cost. Every manufacturer is trying to be the lowest cost producer of solar panels with the highest specs. To be able to do that, corners have to be cut somewhere and the easiest place to do this is the panel backing.
Now about the SunPower panel you asked about.
It uses a polymer backing panel and PET - both to reduce the panel cost but both reducing the quality of the panel compared to a fiberglass panel with ETFE. It also uses Gen II Maxeon solar cells which are older design cells - current production is Maxeon Gen 5 and X series cells.
SunPower makes better panels (Maxeon X series) but the cost is higher. It's not always the case but most of the time, you really do get what you pay for.
ps. The Lensun panels are 21.5-22%, not 17-18%. Still not as high as the best SunPower cells (Maxeon X series 22.7%) but higher than most of the cells out there. When you see a rating of 25%, it makes me wonder where that came from as SunPower doesn't rate their own cells that high. Truth in advertising?