On bouyancy: I worried about this quite a lot last year, not liking any of the options; however, where I sail a full inversion could pin the mast in a sandbank. In the end I got the smaller secumar – it provides more bouyancy than most of the pre-inflated options but is fairly small & neat at the masthead. I haven’t tested it (the reload cost is around £20), I trawled the web and found a couple of cases where it had worked, a couple of cases where it fired by mistake (damp or vibration), but no complaints that it failed. Take this very small sample for what it’s worth.
On radar: I worry about this, but was hoping that someone else had the answer. I presume you’ve seen the annex to the Ouzo report (http://www.maib.gov.uk/publications/investigation_reports/2007/ouzo.cfm) on the likelihood of radar visibility, and the subsequent reflector tests (http://www.ybw.com/pbo/pdfs/radar_reflectors.pdf). These make scary reading but seem to offer little practical advice for something the size of a Wayfarer.