You learn additional spells when you reach certain levels in this class, as shown on the Storm Spells table. Each spell counts as a sorcerer spell for you, but it doesn't count against the number of sorcerer spells you know.

Whenever you gain a sorcerer level, you can replace one spell you gained from this feature with another spell of the same level. The new spell must be a conjuration or evocation spell from the sorcerer or wizard spell list.

Note: this class feature is almost exactly the same as the Mizzium Apparatus from GGR p179. This felt much more thematic than certain set spells and is much less clunky than randomly determining subclass spells every day, which was the original feature. Some might assume this is too strong, but it is only the equivalent of an uncommon magic item.

Another potential issue is that a sufficiently high level wild magic sorcerer might get to the point of effectively knowing every 1st and 2nd level spell. This is not until very high levels, so should not be an issue.

The guaranteed Wild Magic Surge was added to combat the issue that surging relies entirely on the DM.

If the ability to choose is deemed too powerful, the entire feature can be replaced with the ability to roll on the table when the sorcerer chooses to do so. This triggers a Wild Magic Surge as normal. Alternatively, the DC for the save can be increased to 13 + twice spell level to make the casting of any spell a bit trickier.