How each app actually works
HER is a profile app for queer women and non-binary people, with dating on one side and communities, events and feeds on the other. Grindr is a grid of nearby profiles sorted by distance, where anyone can message anyone without matching first. One is a place to be, the other is a way to find someone close by right now.
Who is actually on them
Grindr's crowd is overwhelmingly gay, bi and queer men, and it is the largest queer pool anywhere. HER is the largest space for queer women and non-binary people, but smaller in absolute terms and much more city-dependent. If you are non-binary, both are open to you and HER is the softer landing.
Pace and the tone of the inbox
Grindr is fast and blunt. Conversations often start with a direct question and end within the hour, one way or the other. HER's inbox is slower and warmer, and messages usually reference something on your profile. Neither is better in the abstract, but they are very different to spend an evening in.
What you get for paying
Grindr XTRA and Unlimited mostly buy reach, ad removal and a bigger grid. HER Premium buys filters, visibility and more control over Incognito Mode. On both, the free tier is enough to work out whether your area is worth paying for, so do that first.
Safety and privacy
HER's moderation and community rules make it the calmer of the two, and Incognito Mode helps if you are not out. Grindr's precise distance display has been its known weakness for years, so hide distance if you live somewhere small or unsafe. On both, video call before meeting and tell someone where you are going.