This is actually a really good alternative to Serket for farming. Just set him 2nd last turn (he wont get attacked) and flip him during your turn and summon BEUD and then martyr/union attack for piranha/vassal
With regards to BEUD, I honestly find it better to just run Poly in a Kaibaman deck. The drawback is you don't usually get him out til late game and you have to have a plan to protect all 3 BEWD, but SoI is just as situational and a lot harder to get than Poly. Also, Monster Reincarnation can add a BEWD to your hand to get the fusion off if one is destroyed, or you can use it to Kaibaman a BEWD while you have BEUD on the field.
Shallow Grave doesn't work for fusion monsters sent to the grave that was summoned by summoner of Illusions, just tried it.
Interdimensional Matter Transporter does save the fusion monster from being send to the graveyard.
This is a hard card to use. However if managed to pull this off, the ubewd shd bring big effect of game.