I have a I4 and a BT-C3100, I wouldn’t call one better then the other, but they are different. The Opus has lots of modes and options, the I4 just charges. I don’t feel safe leaving any cells in a charger overnight. The Opus can charge faster or slower than the I4. I’ve found the analyzer functions useful on the Opus I had a pile of older NiMH cells and I used it to sort out the ones that still held reasonable amounts of charge. I’ve got the I4 set up where others in the family can recharge cells because there is no option to set it to the wrong mode.
The best information I know of about these is from HKJ’s reviews,
Yes and, no. With the I4 charging NiMH HKJ found that it trickle charged after it terminated, not a problem if it’s doing that for a few hours, but long term it does do damage to the cells. With lithiums I just chose to err on the side of caution,
Do yourself a favor and just buy the Opus. It will do everything the i4 does and WAY more.
The i4 is simple to use, and changes….period. If you are SURE that’s ALL you want to do then buy that one.
Both are safe (at least as much as chargers of this price point can be), both work.
Read HJK’s reviews on both until you actually understand the basics. IMO it’s mostly a ‘no-brainer’.