Easy weekly bromine spa test?

[spartan]

Hi, we have a bromine spa at home that is used about 30 minutes per week, which we have had for about 10 years. We change the water every 5-6 months as the spa is used so infrequently. We use the floating method with Bromine tabs (1 every 10 days approx), monthly about 20 grams of sodium bicarbonate and this seems to be about all we require to keep the water balanced and stable. Occasionally (every couple of months) I shock the water with liquid chlorine (12.5% strength).

I do have the TFT100 test kit that I occasionally (few times a year) use to double check the readings, check TA or if something seems a bit off and maybe once a year (or if any doubt) i go the the pool shop and they have a proper machine to do more accurate readings, thankfully the readings have been the same so far as what my weekly testing says.

Weekly I would do the quick test with Taylors or equivalent OTO and Phenol Red , in Australia this or an equivalent product can not longer be purchased or is recommended for use but I can get something similar via eBay from Hong Kong. Unfortunately I have just run out and need to get some more. I like this method as its quick and easy and has always seemed pretty accurate when I have done comparative test with another method.

My questions is, is this still the simplest, reasonably priced/accurate method to use in our situation for weekly testing or should we consider something else or are we missing something that we should be doing?

The ebay product is: OTO and Phenol Red

Or something like this for Ph and something else for Cl PH only test

Or I noticed these that look good and easy but not sure how they compare to our current method for accuracy: Electronic Ph and Cl test

Or slightly more expensive and could just be to good to be true Another Electronic test