Pros: This very small charger seems to do it's job quite well.
I use it mainly for charging RCRr2 (with magnets for spacers) and RCR123 LiFePO4 cells, and it seems to work great for those. I also occasionally, charge LiCo RCR123's and 16340's at the 3.6 Volt setting, and "good" cells come off the charger at 4.18-4.20 Volts, no complaints there.

Cons: While the UF/WF-139 has had quite a few complaints over the years, these WF-138's seem to do a better job, and I have to agree.
I really cannot think of anything I do not like about this charger. I do however, pull the cells when the charge is complete (solid green LED) so as to avoid any possible trickle charge.

Other Thoughts: Very compact and comes with a good AC cord.
Not too cumbersome, even with the cord, for packing away when traveling.

Bottomline: If you need a good LiFePO4 charger for RCR2 and RCR123 cells, this is a very reasonable charger to get.
As I said above, it seems to do just as well with LiCo RCR123's, as well.

Pros: It worked OK for a couple of months.
2 independant channels.

Cons: The only thing that you don't want from a Li-ion charger, is that it charge over 4.2 V. This one at the beginning would charge to 4.20 V. Fine. Then, after a few months, it went higher. At 4.23 - 4.24 V I quit using it. And I don't even know if, at 4.24V, the charger stopped by reaching its unprecise limit, or if my batteries'security triggered.

Other Thoughts: Every time a li-ion battery is overcharged, its cycles count goes down a lot. A charger must never damage batteries.

Bottomline: I also bought the Since SE-H001 charger from DX too, which is still much cheaper, and reliably has never overcharged my batteries. The Ultrafire proctected batteries I bought had defect protection. The charger has defect cut-off voltage after a couple of months. Just forget about Ultrafire, it's worth nothing. Some other manufacturers, even cheaper, make good products.

Pros: The ability to charge both 3.0v or 3.6v RCR123s makes this a very versatile charger. Certain lights can only use 3.0v cells due to to voltage constraints, while other lights can accept 3.6v RCR123s (as well as 3.0v RCR123s) this charger can do the job with a little flick of the switch on the side. Great stuff!
I can also use this to charge my RCR2 cells which i am using with the Ultrafire WF606A (1xCR2 or 2xAA light) that i got here, now that light is a monster on CR2s.
Just put the RCR2s in and you can use either magnets (again you can buy them here, or do what i do and just fold aluminum foil into a spacer, that's my cheapskate way of making a spacer)
Havent tried my 14250 cells in this yet though (those were for my Lummi Raw NS)

Cons: None, great little charger for RCR123s and smaller cells.

Other Thoughts: This is a much smaller charger than the WF-139 if you have exclusively lights or equipment that use RCR123s, get this to save space.

Bottomline: I like it!!

Pros: - nice small charger.
- can charge SKU08683 batteries (3.6V)
- also use it to charge 3.0V Lithium ion batteries
- with a modification i chrage CR2 batteries. Length is too short, but with some Nd-magnets it will fit.
- Charging is indicated with red blinking LED; end of charge: green LED.

Cons: - sometimes charging will not start (probabely because the batteries ran out too much). I found out that leaving them for a while in the charger, then removing and replacing them again solves the problem (most of the time).
I am not sure if this is a protected battery issue or a charger problem.
- NEVER forget to check the voltage switch!!!!!!!!!!!

Other Thoughts: - charger doesn't heat up at all: looks well designed
- standard non-EU power plug: use adapter sold by DX or cut wire and attach EU-plug. (works well with 230V)

Bottomline: Nice compact transformer-less lightweight charger