Would reach as a racial trait for my homebrew Mutant race be unbalanced?

Question

I am creating a race of Mutants for my dark fantasy campaign. The core racial mechanic is that each Mutant character picks two mutations from a list. Each mutation gives +1 to an Ability Score and a special trait. Special traits are supposed to be equivalent to ~two thirds of a Feat (I am trying to power-match them to Humans with Optional traits).

I was thinking of one mutation that would give a form of Reach to the character:

Stretched arms: Your upper limbs are flexible and are, or can become, extremely long (e.g., multiple joints, extensible, tentacle-like, etc.). As a bonus action, you can enter in reaching stance until the start of your next turn. While in reaching stance, you add 5 feet to your reach when you perform a melee attack, as well as when determining your reach for opportunity attacks in melee. Your Dexterity score increases by 1.

Instead of giving a permanently increased reach, which seemed potentially too strong to me, the character has to spend a bonus action, which means: (1) it needs to be activated; (2) it gets in the way of other powers (such as off-hand attacks, second wind for Fighters, etc.).

Does this seem balanced?

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It's been pointed out that the Bugbear playable race in Volo's Guide to Monsters (p. 119) has the trait:

Long-Limbed: When you make a melee attack on your turn, your reach for it is 5 feet greater than normal.

So the character would always have extended reach (no need to spend a bonus action), but only for attacks (not attacks of opportunity). This might be a good and more official replacement for my previous tentative formulation (and I assume that being in an official supplement it should be relatively okay in terms of power).

Answer 1

The Bugbear race presented in Volo's Guide to Monsters has a permanent reach enhancement. As long as your new race is not more powerful than the Bugbear (in terms of stat bonuses and other effects) it's probably okay.

For reference, the Bugbear's Long-Limbed feature is as follows:

Long-Limbed: When you make a melee attack on your turn, your reach for it is 5 feet greater than normal.

Coincidentally, the Bugbear also gets a +1 to dexterity, as granted by the trait you mentioned above.

Answer 2

A combination with Polearm Master and Sentinel make this a pretty strong feature, since it allows you to stop the opponent (up to) 2 times, before he gets into attack range:

1. Activate the feature on your turn
2. Opponent tries to get into melee range with you, but you hit him with a attack of opportunity.
3. On your next turn you don't activate the feature placing the opponent outside of your reach. You don't need to move for this to happen so it's possible to avoid attacks of opportunity that could be triggered by you moving back to get the opponent outside of your reach.
4. Opponent tries to get into melee range again on his next turn, granting you another attack of opportunity denying him the possibility of doing a melee attack against you, if you hit.

If you either change this feature to only work until the end of your own turn or if this permanently increases the reach, this combo wouldn't work anymore, since it wouldn't allow you to change reach without moving or makes you unable to use the extended reach for attacks of opportunity. You should apply one of those changes to the feature.