They are just two different brands. There are several, now. These are the two I’ve purchased and used.
Meater: i bought the “meater block” back when it was a Kickstarter. It’s an attractive block of wood that plugs in, and holds/charges 4 separate probes. I’ve never used more than 2 at once, Ave haven’t even taken the tag off one of them. The block talks to my phone by Wi-Fi, and has good range. Sometimes the block and the probe lose contact (after all, the probe is in a big metal box, aka, the oven) but so long as i leave the block really close to the oven, it works.
Mine is old, and only has one temperature sensor. (The new ones have a few, so you don’t have to be very careful about placing it.) It makes a fairly fat hole, and it can be hard to grip the probe to remove it. It’s been pretty reliable.
Combustion: i think this was the first to have a bunch of sensors up and down the probe, including the exterior. It is much thinner, so you can put it in a steak. It’s easy enough to remove. It talks to my phone over blue tooth, very reliably because it doesn’t need to pair. (Don’t buy this is you are worried about your neighbors knowing how hot your meat is) But the range is mediocre, and although either the probes or the additional gadget i bought so i don’t need to use my phone if supposed to use Wi-Fi, i never succeeded in setting it up. It reliably talks to my phone if I’m in the kitchen, but i sometimes lose signal if i go to another room.
The multiple sensors are nice. The external one doesn’t tell you how hot your oven is, because it’s close enough to the roast that the roast keeps it cooler. You do have a very good sense of the exterior temp of your food, should you be interested.
It gives a lot of detail, which you can also hide if you prefer. (So, anything from a colored graph of every sensor over time to a single number for the “core” temperature, which is just whichever is coolest. It also has a magic feature of knowing the integrated FDA food safety charts (integrated time and temp) so if you want to cook your chicken to 150 and know it’s pasteurized, it will tell you that. It’s messier when not in use, because each probe has it’s own charging sleeve, and each one needs to be plugged in. (The sleeve has a battery, and holds a charge for a long time. But just leaving it plugged in is so much easier.)
In practice, i usually use the combustion, and have two of them.
The exterior of these probes (all brands) is designed to be safe in ovens and even in hot grills. But the interior (usually protected by the food) contains a battery and is more fragile. I killed a combustion probe by forgetting that and trying to use it as on oven thermometer.