Solar charger in commercial application based on an LM317 IC
Since you say this is for a comnercial product, I'll be up front about this:  Given the choice between buying your product with an LM317 regulator or a product from your competition using the LTC3652, I'd rather buy from your competition.

You are saving a few cents, and delivering an inferior product.

The LM317 is in all ways inferior to the LTC3652.


The LTC3652 uses Maximum power point tracking (MPPT) to make the best use of the power from the panel.  The LM317 can't.
The LTC3652 is an efficient switching regulator so as not to waste power from the solar panel.  The LM317 is an inefficient linear regulator, whose efficiency gets worse when the panel provides more power.
The LTC3652 is a charge controller.  It has selectable charge termination, and maintains the battery at full charge by monitoring the voltage and switching back to charge mode when needed.  Your LM317 circuit has charge termination, but it depends on the properties of a zener diode and a transistor - making it properly match your battery could be difficult.
The LTC3652 can easily set the charge current - the datasheet tells you how.  The LM317 circuit you have can also set the charge current - does the source of your circuit tell you how?


That LM317 circuit is simpler and easier than the LTC3652 in the same sense that it is simpler and easier to light a campfire on the kitchen floor rather than installing a stove and oven.  It's cheaper, but it sure ain't better.



As already mentioned in the comnents, the LM317 circuit is not a good choice for lithium batteries.

The LTC3652 isn't either, except for LiFePO4 which is explicitly mentioned on Analog's web page.

Both circuits seem to be better suited to lead acid batteries.