The line was "Gill implants, painfull to Use"
But, something that connects that Intimately with the heart & lungs is Not something you'd "remove" casually.
Putting them In would require major surgery.
Removing them would be the same.
When not in use, they would just look (on G'Kar) like a few wrinkles in his skin.
Lyta's, given to her by the Vorlon, almost certainly Didn't hurt to use.
And were totally invisible when not in use.
You have to figure the Vorlons know a Lot more about such things than the Narn, including how to make gill tissue that didn't react painfully to being used in the atmosphere they were intended for.
She seemed happy to remove the breather mask which was probably a bit uncomfortable to wear.
The most noticeable thing about Lyta's gills is that they Didn't show up on a Medical Scanner when she had her physical.
Now, That's a neat trick.
------------------
Do not ascribe your own motivations to others:
At best, it will break your heart.
At worst, it will get you dead."