Virtuoso's Foil - A Bard's Blade (Feedback Wanted)

I made a simple magic item for a Bard. Technically the rules as written don't actually make it easy for a Bard, in general, to use a weapon and also play a music instrument as a spellcasting focus in the same turn if the instrument requires two hands to play like violins. I had the idea for the instrumental bow (what they draw along the strings) could change into a weapon. This way they can attack and cast a  bonus action spell or bardic inspiration on the turn without issue. I realise most DMs would handwaive this away, so I decided to give the item a bit more oomph on top. Hopefully while keeping it simple and balanced. 

Public Share link: https://www.dndbeyond.com/magic-items/12044619-virtuosos-foil

Virtuoso's Foil
Requires Attunement by a Bard
Rarity: Varies

This item resembles a silver bow for playing a stringed musical instrument such as viol, violin, cello or similar. While holding this item you can mentally command the bow to instantly transform into a Rapier whenever you make a weapon attack roll using it. Unlike normal rapiers this one is designed to deal slashing damage. The transformation lasts until the start of your next turn or until you mentally command it to return to the instrumental bow form - no action required. As a weapon the item has additional properties at different rarities as described below.

D&D Beyond Note: Due to system limitations in the homebrew creator you may need to further customise the item on your sheet. To represent the Silvered state click the item on the sheet and select Customise and check the Silvered box. To represent the rarity click the item and select Customise then add the rarity in the Notes box and then add the Magic Bonus, if any, into the To Hit Bonus and Damage Bonus boxes. To more easily roll the extra radiant damage make a Custom Action on the sheet for this, if desired.