I have one Melda plug-in, the stereo-from-mono plug, and it's very good.
However, I had a recent experience that made me hesitate to acquire more. Melda had a recent promo where one plug-in a day was half price for a month. The second or third day of the sale, when I found out about it, had a plug I would have immdiately bought in the sale.
I went to the site (using IE9, a current, mainstream browser) and clicked on the link to get to the sale page. Nothing happened. I reported the problem to Melda, fully expecting they'd do what any reasonable vendor would do, which would be to find some way to treat a customer acting in good faith fairly in response to a problem on the vendor's end. But the response I got was "tough sh*t, there are other ways to get to the sale page ... you should have clicked around until you found it". Actually I had spent about 10 minutes trying to figure out a workaround and never did.
I ended up not buying anything. If a developer blames the customer for their malfunctioning web page, will they do the same when their software doesn't work?