That No-name 2.5x telephoto adaptor will physically fit onto the GL2 - but I highly doubt that such a cheap piece of glass will perform favorably, free of chromatic aberrations and soft edges. Expect to see measurable chromatic distortion in that lens adaptor. The seller does not mention who the manufacturer is - that's a "red flag" right there. The adaptor is labelled as "High Definition". I doubt that.
I don't mean to sound jaded or negative but I have yet to see any of these cheap adaptors perform well enough to earn their keep.
A high quality lens adaptor costs requires exceptional glass and to prodcue a high quality lens adaptor with exceptional glass requires certain manufacturing procedures and labor and all of that costs money. No way around that. Good glass design comes at a price.
I'd prefer to use the Century Optics 2X adaptor http://www.schneideroptics.com/ecommerce/CatalogItemDetail.aspx?CID=1071&II...
It is $525 and well worth it because it does the job without degrading the image quality.
I'm not saying that no-name 2.5x tele adaptor will not suit your needs - you'll probably get the tighter compositions you are seeking and you may find a way to live with the chromatic aberrations and distortion. It's cheap enough that if it fails to fit the bill, it didn't cost you that much to try it out... just don't have a lot of high expectations and you may be satisfied.
don: thanks for your no-nonsense answer. i'm not interested in shooting with cheap junk so i'll give it a miss. i have the canon wide angle (WD58H) & was wondering about getting a doubler of equal quality. thanks for the schneider optics link. thanks also for your prompt reply.