Don't knock hand flying with the FDs on.
Presumably the purpose of practicing hand flying
on instruments is to hone one's scan technique. Scanning involves not only the flight instruments but also navigation needles such as ADF, ILS and VOR as well as distance information.
That is exactly why single pilot IFR demands excellent instrument flying scanning skills - especially as some aircraft do not have autopilots.
On the other hand, if most of this information is fed into a flight director system, the pilots concentration centres on the flight director needles including the tiny square that forms the centre-piece of these two needles. After all, isn't the prime purpose of flight directors to make scanning easier because the one instrument will guide the pilot very accurately providing it is programmed correctly. With autothrottles thrown in as well, scanning of engine instruments becomes a secondary task to the prime task of flight director gazing.
All that being so, it is pointless to leave the flight director on if the pilot wishes to hone his scanning skills, since the whole point of the FD is to reduce scanning workload to the one instrument in the first place.