I do not see how compact matters much here. As far as I understand, the basic reaction used is the same, so that compact design will produce the same number of neutrons per Watt produced as a large one.
Wouldn't the effect of its smaller mass be that the container will have to be replaced more often, more or less in the ratio of the masses of the machines?
We really don't know the practical consequences of this systematic transmutation (for all we know, neutron liberating fusion reactors will never be economic). It's entirely possible the device will have to be replaced more often, I'm just pointing out the less mass in it, the less that has to be disposed of when that happens.
Wouldn't the effect of its smaller mass be that the container will have to be replaced more often, more or less in the ratio of the masses of the machines?