A simple model is used to evaluate the reactor potentiality of direct-drive laser fusion shell targets, irradiated by unshaped laser pulses of an energy lower than a few mega-joules. For single-shell targets a narrow design window in the relevant parameter space exists, which allows for a gain G > 200. Long wavelengths (λ > 2 µm), small aspect ratios (ADT < 30) and small D-T masses (MDT < 3 mg) are excluded. For double-shell targets these constraints are somewhat relaxed; the relevant results agree with preliminary 1-D simulations.