Their primary application is in targeting shielded and/or high-health units to take them out before the sniper bots can be destroyed. Sniper bots should typically be escorted with shields, direct-fire units, and anti-air units due to their fragility (obviously changing somewhat depending upon circumstance).
Due to their long range and accuracy, sniper bots can be very effective at sinking naval units attempting to bombard your base from offshore. Use them in place of Mobile Artillery when greater accuracy is required, such as when engaging small numbers of mobile targets. As they posses a higher DPS, but no Area of Effect when compared to T3 Mobile Artillery, but cost the same amount of mass, these should definitely be used when engaging enemy commanders or experimentals from range due to their much higher DPS and accuracy.
The Sprite Striker has slightly less health than the Seraphim counterpart. Its single fire mode falls between the two fire modes of the Usha-Ah, with higher DPS, longer range and lower ROF than the Usha'Ah's standard mode, and the opposite compared to its sniper mode. Use these in coordination with Shield Disruptors to neutralize enemy fleets with shields.
The Usha-Ah is unique in that it has two modes; one mode is close to a conventional direct-fire mode, and the other (non-default) is full-on sniper mode. Its standard mode is weaker than the Sprite Striker but fires faster, sniper mode is far stronger but very prone to Overkill. A bug (tested in 3606) allows you to get a free (meaning zero reload time) low-powered shot if you switch (back) to the low-powered mode right after firing a high-powered shot; the other way around also works, making the unit incredibly overpowered if you're inclined to exploit this. Also note that the range circle always indicates the high-powered-shot radius, even when the standard/low-powered mode is enabled.
The Usha-Ah is unique in that despite being considered a Bot, it appears to be some sort of hover unit, however it is not amphibious. Its propulsion system seems to be of some unknown origin.