As a scientist I have always relied on thermometers to cook. I have a graveyard of old cooking thermometers including a number of wifi versions. It seems that the probes would get mixed up, the wifi would stop connecting, and on and on. The constant thermometer replacement ended when I started paying more for better equipment. It is the classic example of buy something good once, or buy something of lower quality and keep having to replace it.
I now have several ThermoWorks products and thought I would give you my take on them. They are all good, but each has their strength.
Thermapen MK4
This is an indispensable tool. It is a quick and accurate instant read thermometer. I like the MK4 over the standard because it turns on when you pick it up and the image on the display rotates so that you can read it in any orientation. We have a standard version at my house which I bought as a gift. It works fine as well, but I think the auto start is worth the extra money. When things start going fast it is great to be able to just pick it up and have it go on.
Use: This works in all situations where you need an instant temperature read with a penetration thermometer. It only requires about 1/8 inch at the tip so you can measure just about anything you cook with it. My fish is a lot more consistent since I got it. I have learned the best temperature to remove the fish so it comes out nice and juicy every time.
ThermaQ Two Channel
This is fairly pricey for a two channel thermometer. It was my next thermometer after buying the Thermapen. I have the standard non wifi version with a couple of penetration probes and a couple of ambient probes. It uses the industrial grade Type K Thermocouple probes which come in many configurations and are very accurate. It is also very rugged.
Use: This has become somewhat of an orphan. It was my go to thermometer when I needed more than one probe. I find I like the Signals better (spoiler alert). While it is a great thermometer, it is the one that I would not buy again if I was starting from scratch. It was great to learn on though. I don't think I would have spent the money for a Signals just starting out.
ChefAlarm
This is a great little one channel thermometer and timer. It is great when you only need one probe. I often combine it with my Signals or ThermaQ and use the timer to keep track of elapsed time for the cook. This uses the pro probes which are more than sufficient for backyard BBQ's. It is an excellent choice if you want something that is accurate, that offers replacement probes of differing types, and that works well in both the kitchen and BBQ.
Use: This is my go to thermometer for the large number of cooks where all I need is one probe. I find that I use this a lot. I also combine it with my Signals to give me an additional probe and timer.
Signals
I finally decided that I needed wifi to monitor cooks while I as working. I went with the four probe Signals. So far it has been excellent. Like the ChefAlarm it uses the pro probes which work fine. The wifi connects to an app on my smart phone which monitors temperature and produces graphs real time. I usually run one ambient and three penetration probes off of it. It gives me a really good idea how my smoker is holding temperature, which turns out to be about 20 degree swings. I use an ambient probe at the grill and adjust my smoker setting to give me the temperature that I want, rather than relying on the smoker. You can set alarms which will update your phone with yellow and red warnings and a beep. You can control the alarms from a smart phone, which is nice. I can set warning levels and not have to run down to the smoker to turn off the alarm. I am still working through issues with the wifi. Sometimes I have to power cycle my phone to get it to work. I have it monitoring my refrigerator and freezer at the moment. When I got up in the morning to check the graph the software said it was under the control of another device. I doubt that it was hacked but this is a risk that you have to be aware of with IoT devices. The other benefit of the Signals is that it works as a controller for the Bellows product, which is a fan/temperature controller you can add to BBQ's. Eventually, I think I will try it with my Weber kettle. Unfortunately, you have to drill a one inch hole to install it. There is a good Youtube videos that shows how to place and drill the hole.
Use: Anything where I want to monitor remotely. Big cooks where I need more probes. Any time that I need more than the ChefAlarm will provide.
Industrial IR-IND
This is excellent for measuring surface temperatures. It does what the other thermometers don't do. Lately, I have been using it to check my oil temperature when I am cooking tortillas. It is indespencable for my griddle and also great for getting an idea of how balanced the temperature is in your smoker. Ambient probes are better but it does a good job for quick and dirty measurements. It works great for the pizza oven.
Use: Anytime I want to know surface temperatures such as griddle, oil, pizza stone, etc.
I should also mention that all of the regular thermometers are magnetic and can be attached to your BBQ. The Signals has magnets on the side and bottom. They also have rugged sleeves available, which I use on my ThermaPen and ThermaQ. Add to this great customer support, excellent packaging for shipment, and a small bag of Jelly Belly with each order.