To clarify things : there’s 2 different items that boost your reputation with factions :
Writs are available at Honoured and give you +50%. They are soulbound so only the toon that bought it can use it.
Mandates are available at Reverred and give you +150% (2.5 times normal gain). Since you are already reverred when you can buy those their only use is to be put in the transfer stash and used on another toon.
Basically, after your first toon gets revered with every faction, every following toon can use mandates (well, technically you need 2 toons, one for Kymon and other for Order) right from the start.
And while we are talking about potions of clarity they work even when your experience is already maxed and you want to level up devotions faster as your devotions also gain XP.