not true, you just haven't considered other monsters effects which might stop them from being summoned from GY.
You can summon Lady Diamond perfectly fine with this, but to do so, you must've had her fusioned summoned first and then if she's in GY she can be summoned. Also can't summon her more than once per turn.
for everyone who says this card doesn work properly:
-this card does exactly what it says, but the conditions of gem monsters in GY may stop you from summoning them
- Lapis fusion monster can discard Lady Diamond for example, but if so, Lady diamond can't be summoned from GY anymore because of her effect "Must be first fusion summoned"
- also if you do fusion summon Lady Diamond and send her to GY, still you can't bring her back because she can only be summoned Once per turn
This is a very good card IMO and although seemingly simple to use, the fusion monsters' effect must be considered as well!
I used gem-knight lapis lazuli to send gem-knight master diamond to the gy, then used this card to tribute my gem-knight iolite but i cant get my master diamond back on field stuck taking that iolite back to the field, is there something wrong?
All Fusion monsters that can be revived from the Graveyard, cannot be revived if they have not been Fusion Summoned properly first.
Same thing also applies to Synchro/Xyz/Link monsters, for example you cannot revive Stardust Dragon with Stardust Flash or Stardust Shimmer if Stardust Dragon was sent directly from the Extra Deck to the Graveyard.
This card doesn't work well. Sometimes when you tribute a powerful gem-knight, it doesn't let you summon it again (in order to attack twice or use its ability twice). Sometimes it only lets you summon the other less powerful gem-knights in your graveyard, all of them except the one you need to summon. What a pain!
Some of the Fusion monsters, like Lady Diamond for example, have the effect that they 'can only be summoned once per turn.'
actually amazing card, you can choose the card you just tributed to attack again.
combo with fragment fusion or even flash fusion if you think you can swarm the field very fast and use this card to negate the destroyed requirement of both card.