The Holo Grenadier is a valuable Pilot to have. Not only does his ordnance provide good area-of-effect damage against infantry units, but the hologram he projects covers his advance, usually letting the real Grenadier bombard the enemy from relative safety for a short time before becoming fully exposed. Note that the real grenadier can still be fired upon by anyone - or anything - smart enough to target him first before his hologram. The Holo Grenadier will also require a couple seconds to spawn his hologram before he actually heads out into the battlefield, so expect a short delay every time he is summoned.
The Holo Grenadier's grenades displace enemies, making them especially effective against the Gunner or slow-firing attackers like the Boomer.