Use the OTO color comparator just for the pH test. Don't bother using it for CL.
I do not agree with that advice. The OTO chlorine test is in the TF-100 for a reason......it is not just haphazard.
1. There are times when newbies don't understand how to use the FAS/DPD correctly or they are confused by the results. The OTO test is about as bullet proof as you can get to detect if you have chlorine in your pool.
A newbie may report 3.00238 with the FAS/DPD or gets a zero result when, in fact, the FC is so high it bleaches out the pink. None of this occurs with the OTO. It is virtually never misinterpreted and can help many newbies get on the right testing track. It is completely reliable......just not accurate.
2. Some, not many but some, cringe at the cost per test of the FAS/DPD yet want to check the FC daily (and they should) The OTO fills this bill perfectly and is VERY fast to boot.
I know some simply like the precision of the FAS/DPD and don't mind the cost and it's all they use. Most of the time, all I would use is the OTO. My chlorine was quite stable and it was easy and quick for me to read the OTO pretty close to daily and also easy to see a darker or lighter yellow than I saw yesterday......I tested for changes/trends and not so much precise ppm's.
So, the TF-100 gives you some options. I know that comparator takes up a lot of space and the TF-100 could drop that comparator and replace it with just a pH comparator block but I think giving the customer the option as to which CL test he cares to use is worth it.
Like mknauss, I kept my CYA bottle separate. If you are testing much more than about 6 times yearly for CYA, you are testing it too much.
(Oops! sorry! I didn't answer OP's question.....you should believe the FAS/DPD test.)