I don’t know, but between two houses we owned with pool/spa combos, none of us ever experienced any detrimental health consequences as a result of using them. We didn’t have a lot of people in them, typically only our little nuclear family and an occasional friend of kids, but our experience was perfectly fine/safe/enjoyable.
We’ve had one for a couple of years and love it. It’s easy to maintain and keep clean. DH tests the water every few days, then just adds a few drops of whatever is needed. He says it’s MUCH easier than the above-ground pool we had when the kids were young.
When I got back from my overseas trip yesterday, the first thing I did was jump in the tub with DH and drink wine.
We have an official home office policy. If it snows during a work day, we go out and sit in the tub.
We use it year-round - we just lower the temperature during the summer.
We’ve had a Sundance for 12 years and my husband loves it, and has had no skin issues. He has back issues, so uses it several times each week.
We’ve only had 2 service calls in that time and he’d tell you that it’s very low maintenance. I don’t really use it. I agree with the poster who said you’re either a hot tub person or you’re not.
We’ve had a hot tub for 25+ years. Dh really enjoys it as do the kids. The place we bought it services it quarterly and, while we’re supposed to do something more often than that, we don’t. Have never had a problem but it does continuously circulate and it’s not used more than once very week or two, sometimes less. In the early years, we, naively, ran it all the time and it took me awhile to figure out why our electric bills were so high. Now we just run it at the lowest level possible so it does circulate but is about room temperature. Thus, we need up to about 4 hours to heat it up but the trade off is definitely worth it. Our electric bill went down $100/month once we made the switch.
I agree about the cover and I’d also ask about the cost to run it and what the options are to keep it “healthy” if you’re not going to use it often. Turning it off completely is not a good one we’ve been told, assuming you do plan to use it.
This would be a big “con” for me! 
Yowie!!
I use the hot tub at the pool where I take water aerobics several times a week with 8-12 other people in the class. I’ve never heard of anyone having a health issue due to the hot tub. And this bunch wouldn’t keep quiet about it.