Due to the wording of this card's effect it does not end when it leaves the field, so even if "Mystic Fairy Elfuria" leaves the field for any reason, you and your opponent cannot summon any other Xyz Monster with a monsters different to the Level used for its effect.
Just like "Psi-Blocker" this card's effect also stacks if it leaves the field and is summoned again on the same turn after already being activated; or another copy of this card is on your side of the field and it too has its effect used that turn.
You can also Xyz Summon a monster yourself to your side of the field and then activate the effect of this card afterwards without issue.
With the wide variety of WIND-attribute monsters available in a Gusto deck and given that deck archetype is more tailored to using Synchro Summons, this card can easily help restrict your opponent's Xyz Summoning options while not hindering your own deck.
Reveal "Gusto Egul" for this card's effect since there are almost no Rank 1 Xyz Monsters that are used by most duelists (except "Slacker Magician"), so that your opponent cannot Xyz Summon at all in most cases.
However this can be quite ineffective, since most of the commonly-used Xyz Monsters are Rank 4 anyway.
Heraldic Beast decks can prevent this card from being destroyed by battle when using it through playing "Heraldry Change" to stop the attack and end the Battle Phase, while also benefiting through gained field presence at the same time from the Special Summoning effect of "Heraldry Change" (perhaps even of the same Heraldic Beast monster you revealed for the effect of "Mystic Fairy Elfuria").
Wind-Up decks are very vulnerable to this card's effect: simply do not use a Level 3, 4 or 5 monster card as the WIND-attribute monster you reveal to prevent them from choosing a large portion of their Xyz Summoning options (if not all of them).
With the exception of "Wind-Up Shark", which is commonly played in this deck type, it is not often that your opponent will have monsters equal to or higher than 1500 ATK strength that aren't Special Summoned on the field, so the chances of "Mystic Fairy Elfuria" surviving for an extended period of time are good too (with appropriate Spell/Trap defense of course to support it).
Inzektor decks are vulnerable to this card's effect (just like Wind-Up decks) if Rank 3, 4, 5 and 6 choices are prevented. However with their stronger monsters, more readily accessible card destruction effects (i.e. "Inzektor Hornet") and ATK boosting effects it will be difficult to keep "Mystic Fairy Elfuria" on the field to repeatedly use its effect, so remember to plan around it.
Hieratic decks are vulnerable to this card's effect too if Rank 5, 6 and 8 choices are prevented, but they can more easily work around it as many of the monsters in that deck type are 1500 ATK or higher and will destroy "Mystic Fairy Elfuria" the first chance they get to limit the long-term obstruction.