They are both PPK solutions, not RTK. This basically means that a little work afterwards is required to perfect the satellite information and then apply those values to the images rather than the RTK values being written directly to the image live as with the Phantom 4 RTK. PPK is actually the more preferred method amongst professionals that require consistent and verifiable data. I use a Teokit but would stay away from it unless you are very comfortable with electronics and taking things apart.
My favorite is the Tuffwing.com snap kit with a Vanavara AShot board, but the AShot is apparently is no longer sold by itself so this may not be an option. I would sure shoot @VanavaraDigital a PM though in case they can work around it with you. I wish more people considered this option because it really is the most modular and cost effective. You can easily take it off if you don’t need it or are in a situation where the flying is a little dicey. You can still get the stand Tuffwing kit from their website, but aware that it is stated to only work with the M+ model which is L1 only and it uses a light sensor to record the events of the photos which has a 200-300ms delay that needs to be accounted for. This does not occur with the AShot board. The receiver purchase is separate so all together the kit is about $600. I have yet to test the kit with an M2, but will be doing so today now that I have a reason to.
The TopoDrone kit seems very good in the fact that it is pretty easy to install and L1/L2, but is also a bit pricey at $2k for what it does.