While I have, in this thread, cautioned against using the really low-powered triodes in single-ended topology, I am sort of in agreement with clio09 about the possibility that someone may be satisfied with the result; it all depends on the specifics, such as how easy a load the speaker is, type of music, how loud one listens, how large is the room, and most importantly, what compromises one is willing to make. There is always compromises involved, no matter the budget or any other consideration. If one does not highly prize extremely deep and tight bass, or if one listens mostly at modest volume levels, a SET amp might work even with speakers not designed to work well with this type of amplification. Unless one listens to head-banging music most of the time, the average listening level will be such that one would be using less than a watt with even inefficient speakers. So, the question is: how important to you is it that the sound system performs well for the comparatively shorter time it is asked to deliver higher volume?
When I listen to large choral works with my 6.5 watt parallel 2a3 SET (Audio Note Kageki) driving 99 db/w 8 ohm speakers, I can tell that on peaks, the sound is becoming a little bit muddled and is sounding compressed (not really getting much louder even though it should be). But, for almost all other types of music, the amps deliver all the power I need, and given my priorities (I demand good dynamics and a full and lively sound at LOWER volume levels), the compromise is worthwhile. The same holds with my other low-powered tube amps.