South Korea recently sold 120 of its locally designed and made K99 155mm self-propelled howitzers to Poland. South Korea has already sold 350 to Turkey. While superficially similar to the American M-109 the K9 is a heaver (46 tons versus 28 for the M-109), carries more ammo and has twice the range (up to 56 kilometers in part because of a barrel that is a third longer). There is more automation on the K9, so it has a crew of five versus six on the M-109. South Korea thus joins Germany in their effort to build a suitable replacement for the elderly M-109 design.
The United States sought to build a replacement for the M-109 (the 56 ton Crusader) that was very similar to the K9 but was too complex and expensive and the heavier weight was seen as a disadvantage for a country that has to ship its armored vehicles overseas to use them. For South Korea, Turkey and Poland that is not a problem and more heft (and protection for the crew) is an advantage.
One American innovation K9 users will probably adopt is the GPS guided Excalibur shell. This smart shell entered service in 2008 and changed everything. Excalibur has worked very well in combat, and this is radically changing the way artillery operates. Excalibur means 80-90 percent less ammo has to be fired to destroy a target and this results in less wear and tear on SP artillery, less time needed for maintenance, and less time spent replenishing ammo supplies and more time being ready for action.
Because of Excalibur (and other precision munitions) since 2001 operations in Iraq and Afghanistan provided very little work for the M-109. The lighter, towed, M777 has proved more useful, especially when using the Excalibur shell. Currently, the army plans to keep newly upgraded versions of the M-109 around until 2050. The army plans to acquire at least 551 upgraded M-109s by 2027, reflecting the impact of the Excalibur shell, and the number of older M-109s that are still fit for service. The M-109 was a solid design, which is pretty clear from how difficult it's been to come up with a replacement. So, in the end, the army replaced the M-109 with another M-109 upgrade and is still seeking a replacement for that.