You must provide warm water to maintain the health of your betta fish
Tap water high in chlorine and heavy metals is extremely toxic to fish, and Bettas are no exception.
And believe it or not, the bigger the tank, the easier it is to maintain. If you want a truly easy to maintain betta tank, why not buy a 10 gallon with a lid (lid is important, bettas are notorious jumpers) and heater? Do a 25% water change once a week (make sure to use dechlorinator) and you should be golden. More room and healthier environment for your fish, less work and much cheaper than that little tank for you. Just make sure wherever you sit the tank is sturdy, water is 8.5 pounds a gallon, so with rocks and everything you're looking at about 100 lbs. for a 10 gallon tank.
Also I would assume I'd need a heater. Is there even a type of heater that would work for this kind of set up? Definitely too good to be true. First, it's too small. Bettas can be kept in small bodies of water, but I don't recommend any less than 2 gallons (many websites will say even bigger, a minimum of 3-5 gallons). Maintaining water quality is important to fish health and I wouldn't trust this thing from malfunctioning.
Why do betta fish need a water heater? - Quora
Do Betta Fish Need a Heater and Filter in their Tank? | PetHelpful
BETTA TANK Contrary to popular opinion a Betta cannot live in a BETTA BOWL or such similar sized tank. I would say the minimum for a truly happy Betta is 5 gallons. The Betta bowls or cute little containers they have come up with now are impossible to heat or filter and we will come to that momentarily, but Bettas are Tropical Fish and as such, need to be kept in heated and filtered water.BETTA FILTER Here again, because the Betta is a Tropical Fish and especially because you love your fish and do not want to subject him to having to live in a sewer, you need a GOOD filter in the tank you will be housing him in. This means chemical, biological, and mechanical filtration - no undergravel filters (UGF). There are a lot of types of filters out there but not all of them are appropriate for a Betta. Bettas are not given to being in a strong current so you need to find a filter that is adjustable to the degree that it provides a ripple or small waterfall - not a torrent. They do like some movement to the top surface of the water as they are one of the Labyrinth fishes. These fish have an organ on the top of their heads that not only allow them to breathe air like we do, but demands it. So if dust, scum or anything else builds up on the surface of the water and the Betta is prevented from reaching a clean surface spot, he will drown. He also uses his gills so he can remain underwater for a time, but if you watch your Betta he will go to the surface and "butt" the surface with the top of his head, this is his "breathing air". A lot of owners provide a tall plant for their Betta to sleep in at night so they won't have to swim so far to "breathe".BETTA HEATER Being Tropical Fish, Bettas need to be kept at a temperature of 78 degrees F (25 degrees C) at a MINIMUM on a consistent basis. It would be much better to aim for 80 degrees F (26 degrees C) to make them even happier. This is very important as the Betta seems to be especially prone to some of the cold water conditions such as Ich and Finrot. These diseases are primarily prevented by keeping the tank temperature at steady and proper levels. and water parameters good.Many people will tell you that their bettas do fine without a heater in the tank. And it is true that they can sometimes live without a heater. Remember though, for your fish to thrive, they need to live in water that is always between 74 and 80 degrees Fahrenheit. The only way to ensure this is the case is to have a reliable heater and to check the water temperature regularly.