Hi @KT27, welcome to the Sonos Community!
Generally, if you don’t have a Sub or Sub Mini, you’ll notice a big increase by adding either of those devices to any setup. I would say it’s worth adding if you’re noticing a lack of bass, especially if you’re listening to music where it should be more prominent.
One thing I would suggest before buying however would be to adjust the bass of your Era 100s in the Sonos app. You can do this by opening the app and heading to Settings → Era 100s → EQ, then adjust the slider for bass. If this makes a noticeable difference and sounds good to you, you might not need to get the Sub Mini.
You could also buy the Sub Mini from Sonos.com to try and if you don’t like it, return it under our 30-day return policy.
I hope this information helps!