I own a Lazy Spa and have had it 4 years and love it. My advice would be rent one for the summer, see how it works out.
Water temperature coming out of a hose pipe attached to a cold tap is around 17 degrees ish. It needs to get up to at least 36 for it to feel hot. The pump will raise the temp roughly 1 degree per hour for mine which is 900 litres. I would say you need that pump on for 17 hours to reach temp. It is a 2kw pump. The water temperature won't drop all the way back down to 17 when you turn it off but you need to decide if you let it drop as far as it can before heating again or you keep it ticking over in the mid/high 20s so when you want it, it takes less time to heat.
Maintaining it isn't hard but it isn't as straightforward as you dip it, it says you need to increase the Total Alkalinity so you work out how much TA plus to add using the table on the product and yet that they throws out the Ph too high. What I found, because it is me that deals with it all, is that you need to go slowly with it. People rush, they want to just get in and this isn't that either to start with and also you can't just decide at 4pm you want to use the tub tonight.
Position, sun or shade, insulation under the tub, insulated covers etc will all cost and add to this. Personally, this is both a nice thing to sit in but also a place I need for pain therapy. Mine is inside a large shed so private for changing, I can be in there no matter the weather. I know people will say just take a bath but another person cannot join you in the bath and you are stuck in one position and the water would never be up to your neck nor does it keep the temperature. I can be in that tub for 4 hours and with the pump and heat on it stays at 37.
The biggest factor in all of this is the electricity to heat it and if the novelty wears off. As I suggest, rent one.