Only 2 reviews and 50 downloads… and the app forces you to grant access to Do Not Disturb, Calendar, and other permissions before it will open. That’s a no-go for me.
(I stopped when it asked for the calendar as that’s far to private a thing for an NFC app to require)
Many years later, NFC integration with iOS has finally arrived. 
The iOS 13 “background”/built-in NFC reader capability is only for the two newest devices, iPhone XS and XR. For those of us with older phones, we may still have to use an NFC reader app.
However, you can do this now with an iPhone 7,8, or X using the free App “Simple NFC” on iOS 12 (and maybe even iOS 11). This app has the ability to invoke a HomeKit scene by scanning an NFC tag.
I grabbed these tiny NFC stickers that seem to work well: https://www.amazon.com/dp/B01J2U3DIO/ref=cm_sw_r_em_api_i_c_fCRjDb7D0MTJT
As far as I understand, you can use any Ntag213 tags that are NDEF formatted.
Writing to the tags cannot (yet) be done on iOS device. But I have an old android tablet (Nexus 7) that has NFC, and there are free apps that can program the tag (I used “NFC Reader tools”).
The iOS app “Simple NFC” has instructions in their settings for setting up the Homekit Scene invocation. But essentially, you just program the NFC with a specific URL that will invoke “Simple NFC” and it in turn invokes the Homekit scene (the scene name is in the URL).
The only limitation is that you have to open the 'Simple NFC" app to scan the tag, but once you scan, the Homekit scene defined by the tag runs automatically. The app has on option to start the scanner when the app opens, so the whole process still only takes one tap to open the app and start scanning.
What I would like to see in a future watchOS is the ability to just scan with the watch without having to open any apps or anything.
My plan for using these sticker tags is to put them, for example, on the outside of the door and garage door, which have Homekit enabled locks/openers (via HomeBridge). I may also put one on the wireless charger on my night stand so I can run my Bedtime/Lights Out scene automatically when I place it in the holder.
So i after reading to install the 3 apps - NFC Trigger, Sharptools and Tasker, configuring them together, I was able to make this work to unlock/lock doors, and turn on/off lights with NFC tap.
I think you have to install Tasker first, then Sharptools. Sharptools links Smartthings hub to phone. Then NFC Trigger will trigger routine in tasker which runs a routine in Sharptools.
I have a video in action
It is not expected to be a security risk at all because the NFC tag does not store any personal information. It only stores a trigger routine that tells the smartphone what tasks to run. In this case, when the NFC tag is tapped, it triggers actions and routines to run on the smartphone to do home automation tasks, such as unlocking door locks, turning off the lights, etc.
The smartphone must be logged in to the Samsung Smartthings app in order to function properly, and the phone itself likely is secured by Iris Scan, or PIN.
So the NFC Tag is useless to a thief.
Update as of March 2022: The app required to download for the NFC tag is: NFC Tools - Pro Edition by wakdev developer, Tasker by developer joaomgcd and Sharptools Tasker Plugin and Widgets for smartthings by Smarttools, all downloadable from Google Play.