I am relatively new to this game. On my first level 20 character I took the finding dragonmarks because they sounded really fun. In practice they haven't turned out that way. I'd like to take a moment to lay out my case for this primarily for new players considering taking these marks. I will add suggestions to keep the criticism constructive.
Keep in mind that for a feat, toughness which gives you 22hp is considered a low priority for most builds.
Least Dragonmark of Finding: allows you to find useless items in breakables. I have only used this ability about 100 times but i have never found anything remotely useful. Currently this is essentially a dump feat that you take only to get access to the next tier of dragonmarks.
Suggestion: completely scratch the current system. For starters add just 12 items, 10 common, 2 rare, that you can find in crates. Make them something like a +4 stat potion that stacks and lasts 10 minutes, giving you a small but fun boost for part of 1 adventure. Add a ddoor wand with 1 use, potion of heal. Keep things bound to the dungeon. 22hp can save your life in a dungeon, so should this feat be able to.
Lesser Dragonmark of Finding: casts a weaker version of the level 2 spell knock. While this dragonmark isn't as useless as the least, it is pretty weak. Any rogue, wizard, sorceror, and anyone with UMD (probably half of characters when added together) do not need this at all, and for the rest they can just use a knock clicky. For those who can use it, it will often not open the locks you need to open. I went to prison of the planes with my wizard and was forced to memorize knock after this failed to open the door on a roll of 20, at character level 20 (knock worked just fine).
Suggestion: In order to be worth a feat this ability should do something that can not be replicated with a cheap clicky. Off the top of my head, perhaps the ability could reduce trap damage by 50% for 10 seconds. The idea being you would be able to get to trapped chests better. Perhaps it could highlight treasure chests on your map, not sure what the coding challenge would be there but perhaps not so bad.
Greater Dragonmark of Finding:
This will be a long one. First let me put this out there, I approximate the buff check to be a DC 15 charisma check but this could be way off as it's only based on the experience of a few players with moderately varying charisma scores (22, 24, and 28)
This is the sole reason to take the dragonmark of finding series right now, and it is not a very good one. It allows you to 'bless' a chest, giving it +2 levels (not exceeding 23) The exact mechanics of the loot system have not been disclosed but from my experience of opening thousands of buffed and unbuffed chests, and from what the devs have said, I have a pretty good idea how this works. The +2 chest level primarily effects the things that drop out of every chest. The random item with have a higher + in the top right corner which the loot system uses to generate it's properties. In short you will find a +3 holy light crossbow of pure good instead of a +2 version, or you will find a +2 holy burst bastard sword instead of a +2 holy bastard sword. You will get more greater essences when you find greater essences, and you will get a higher renown reward when you find a renown award. As for the things that players most want to find such as named loot, and rare global loot drops, for the most part this won't help (the exception being that you can't find ML 6 world loot in a level 4 chest but you can if you buff it. Unfortunately this effect actually reduces the chance to find good items in most cases for example if you get worldloot in a ML 6 chest you have ML 0 to 6 items that can drop, if you buffed it you have perhaps ML 0-8 items that can generate and thus you reduce your chance to get the good low level items that are useful and valuable. It is possible that the loot generation scripts could use the chest level to increase the chance for named item drops but as it stands now I see no evidence circumstantial or otherwise to suggest this is the case.
Another slight drawback is that it takes significantly longer to bless a chest then it does to open it so the majority of the time you don't get to use it unless you make a big fuss as one of the 5 party members inevitably opens the chest immediately. And it's hard to justify making a big fuss when there is very little benefit to the party. Also a warning to new players, for most builds taking these 3 feats will cause many players to consider your build 'gimped' and not party with you. I've even been booted from a party for having this and not a feat they considered mandatory. As it stands as a single feat the greater dragonmark of finding is worth it on some characters, primarily for the increased renown generated on buffed chests, unfortunately you have to dump 2 feats to get it currently.
Suggestion:
Now that I think about it I wonder if there is a single dragonmark series that wouldn't be more balanced than it currently is by squishing them into one feat and making the higher abilities unlock at higher levels as is needed for balance. This solution would probably be easy for development and create 7 new usable feats.