The first conclusion is that there is no substitute for size when it comes to radar reflectors. The devices that offer smaller size and lower windage simply don’t work as well. With regard to the Firdell Blipper, it is a well packaged and clever device, but the models tested were not large enough to have much real value aboard a vessel. Larger versions would accomplish what GEC Marconi claims, but are not practical on small vessels.
The Davis Echomaster (in the "Double Catch Rain" position) and the Lensref performed the best of all of the devices tested. The Lensref has no nulls, which is a tremendous advantage in terms of being seen, but the overall reflectance is marginal. If a Lensref is fitted on a sailing vessel, it should be gimbaled or made adjustable. The Davis Echomaster had stronger peak reflectance, but also large holes, which means that a large target would not consistently be presented on a ship’s radar.
None of the reflectors would be more than marginally useful in offshore situations where only S-band were being used, except perhaps in calm sea conditions.
The marginal performance of radar reflectors in general does not mean that they should not be carried. On the contrary, anything that improves a vessels radar visibility is worthwhile, particularly short-handed vessels and those without radar themselves.
Beyond that, it needs to be again pointed out that the best defense where shipping is concerned is a good offense. A ship’s radar may only see a sailboat three or four miles away, but that same sailboat can typically see the ship 12 miles away by radar, and visually at least 8 miles away in clear weather. The small boat is both better equipped and more highly motivated to avoid the potential collision.