Many people do not do well having ALA or LA as their first chelator. It either doesn't work for them or their symptoms become too strong.
If I was doing chelation, I'd start with DMSA (100mg per day max) for the first 6 rounds and then do a combination of DMSA/ALA afterwards.
You can screw yourself up with any chelator if:
1) You take too much. It's best to start slow, 12 mg every 3 hours, total of 100 mg of ALA per day.
2) Your mineral levels are too low. It's best to check your hair levels for minerals before starting and mineralize for any deficiencies.
In any case, 8 hours after your first dose of a chelator, you should do a urine analysis for both heavy metals and (good) minerals to get a baseline test and to detect any deficiencies. Mineral deficiences are serious and you can end up in the hospital or causing yourself permanent harm. You may need to re-mineralize for 1-3 months before continuing.
I 100% disagree with not taking breaks. You need to take breaks because chelators chelate both good and bad metals out of your body. Any chelator should be taken for 2 weeks in a row maximum, followed by 2+ weeks off. Most people chelating should only do 3 days in a row, especially to start.