You should also remember that your investment in NFTP is protected by the fact that NFTP runs on wide variety of hardware, with the same user interface: from lowly 386 machines to high-end Alphas. Many NFTP users who had to switch from OS/2 to Windows or Linux have appreciated versions for those OSes (and they got them free of charge!) Nowadays many computer professionals run more than one operating system: FreeBSD and Solaris as Internet/intranet server, Linux as perfect Unix desktop, Windows for games/office applications, BeOS for great multimedia toys. Thus single NFTP license will buy you FTP client with consistent user interface across all platforms! Nine apps at the price of one!
Do not forget about support. Registered users get their problems solved quickly (as long as my resources permit, typically during several days), including custom versions to address particular bugs.
NFTP is shareware. This term means you can use and test it thoroughly to find out whether NFTP suits your needs or not, and then decide whether it is worth the price or not. Contrary to typical 'commercial' software, there's no shrinkwrap or printed manual, but you can test the software at no obligation during 60 days.
The binary NFTP code is freely available for download; the purchase only gives you the registration key. One license covers all versions including future ones and all platforms including future ports. E.g., if you have registered NFTP and then later switch to BeOS for Alpha :-) and if I port NFTP to BeOS for Alpha, you already have the license for it! This does not guarantee that I will port NFTP to every operating system in the world, of course. My current policy is to release versions for all operating systems simultaneously. Sometimes there might be delays with systems I don't own (these include Alphas and RS/6000).