I haven't looked at the 6Moons reviews Charles referenced, but I would caution that some of the First Watt models are suitable for use only with a relatively limited number of carefully chosen speakers.
The comparison chart on this page
provides a good starting point. The "output ohms" column refers to the output impedance of the amplifier, output impedance corresponding to damping factor divided into 8 ohms. Several of the models have extremely high output impedances (and therefore extremely low damping factors), which cause them to act essentially as current sources (rather than as voltage sources, which is how most solid state amplifiers behave). Most solid state amplifiers, including your X250.5, have near zero output impedances, and high damping factors. Most speakers are not designed to be driven by amplifiers having very high output impedances. There are exceptions, of course.
As you can see from the numbers in the chart, that is particularly a concern for the F1, F1J, F2, F2J. And to a lesser degree (but one which may still may be significant with many speakers) for the SIT-1 and SIT-2.
The manuals that are available at the First Watt site for many of these models discuss what kinds of speakers tend to be suitable for use with them.
Also, note that none of the models listed are rated to provide more than 25 watts into 8 ohms.
Hope that helps. Regards,