I have Sampletank, and also some cracking soundfonts (many way better than Sonic Synth sounds). Was this the answer for occasional soundfont use?
Interface: A bit amateurish looking. Irritatingly only 1 sound name is displayed on screen rather than a list, and a rotary knob (what is it with VST programmers that standard scroll bars are not used?) "scrolls" through the available sounds. Does however allow you to adjust the pitchbend range. It usefully lets you know when a sound is loaded and ready to play - other VST programmers please note!
Sound: Free sounds are very poor quality and do not begin to compare to Sampletank's. Sample Farm even tells you: the free sounds are rubbish, but you get what you pay for - hardly an inducement to upgrade! You can only load very small soundfonts, you can't even try any good soundfonts you might have.
Features: could do with being multitimbral. As far as I can see you have to open multiple instances - I couldn't get this to work in Cubasis. No effects.
Sounds: few low quality soundfonts. But if you upgrade there are plenty of higher quality ones on offer. The low memory limit is far too inhibiting - why would anybody prefer this to Sampletank?
VFM - it's free.
Stability - it did what it said on the tin.
The programmers could learn from Sampletank/SS, who give you a few really great presets, and have you looking for more. I was generally underwhelmed with Samplefarm, and have uninstalled Samplefarm free. For playing my soundfonts I will stick with Jeskola XS-1, despite its minor problems relating to forgetting presets. It sounds better, is multitimbral (4), allows layering, and has a useful reverb, chorus, portamento, and a (rather crunchy) distortion. Worth the $50.