Units which come from the circle of sand are seemingly the basic units of the Alin in Rise of Legends but all have their strengths in combat. All units which come from the circle of sand can be upgraded via the sand spire structure.
Note about Ramping unit costs: Ramping increases the cost of a unit for each unit of a same type that is built. For example, a heartseeker begins costing 45 wealth. With a ramping increase of 3 wealth, the second heartseeker would cost you 48 wealth; the third 51 and so forth. It's wise to have a diversified army because of this increase. Some units have extremely high ramping costs.
Desert Walkers:
Initial Stats: Ground Attack: 6 / Siege Damage: 2.4 / Range: 2 / Health: 113 / Air Attack: None (but can be upgraded) / Speed: 34 / Line of Sight: 12 / Size: Small / Armor: Light / Attack Type: Skilled
Cost: 43 Timonium. Ramping increase of 3 Timonium. Population cost 1
Desert Walkers are your basic infantry unit. Initially, they don't have a ranged attack but they can be upgraded at a sand spire. Upgrading to glass bolts increases their attack damage by one and allows them to fire glass bolts at a range of 8. This also allows them to attack air. The glass bolts upgrade also adds an additional 4 hp to them but it's nothing to be excited about.
They come with two combat stances initially: there's the basic stance, which does normal damage and the whirling blades stance which increases damage infliced but also damage received. The second stance isn't much recommended unless you're fighting something that can't fight back as the desert walkers' survivability is already quite low. These guys are mainly good against other infantry or otherwise lightly armored opponents. They can be upgraded to have an additional stance, one with sand, which makes them untargetable and passive (they won't attack). This could be good for damaged units fighting in your territory if you have the vigor technology track researched at all.
Overall, desert walkers will be useful to you. They are the Alin units to go to when you want to raid a neutral camp and they're good at distracting the enemy for a short time while your stronger units do their work.
Heartseeker:
Initial Stats: Ground Attack: 5 / Siege Damage: 2.4 / Range: 14 / Health 175 / Air Attack: 10 / Speed: 42 / Line of Sight: 19 / Size: Medium / Armor: Light / Attack Type: Piercing
Cost: 45 Wealth. Ramping increase of 3 Wealth. Population Cost 3
Heartseekers are good overall support units, providing they don't get into the heat of combat. Their light armor and fairly low hit points make them vulnerable to attack. They are best suited to hang back and pummel the enemy from afar. Early-game you will find them quite easy to recruit because they require only wealth.
Heartseekers' strength lie in their anti-air attack. In large engagements you'll be pleased with their performance if you focus-fire on air units and let them do their work.
Scorpion:
Initial Stats: Ground Attack: 10 / Siege Attack: 8 / Range: 2 / Health: 320 / Air Attack: None! / Speed: 48 / Line of Sight: 9 / Size: Medium / Armor: Medium / Attack Type: Piercing and Pounding
Cost: 60 Timonium/35 Wealth. Ramping increase of 4 Timonium and 2 Wealth. Population cost 4
Requires Large City
Scorpions excel at front-line combat. Their good hit points and medium armor make them survive quite well. Scorpions are probably one of the first units you should be building once you get to large city because you can use a single scorpion to trample massed enemy infantry while the others do their work. Their attacks are effective against all armor types to some degree, suffering no major penalties.
Scorpions are great damage absorbers. I highly recommend that, if facing many infantry units, you micromanage some trampling to score infantry damage. Scorpions work very well in groups for this reason. They are great at helping (not solely leading) attacks on neutral cities early in the game.
Sand Dragon
Initial Stats: Ground Attack: 10 / Siege Attack: 8 / Range: 14 / Health: 700 / Air Attack: 13 / Speed: 52 / Line of Sight: 18 / Size: Large / Armor: Heavy / Attack Type: Universal
Cost: 250 Timonium/50 Wealth. Ramping increase of 20 timonium and 5 wealth. Population cost 6
Requires Great City
Sand Dragons are adept at killing almost any type of unit. Their attack is a simple shot that delivers splash damage to the surrounding area. These guys can knock down entire units of infantry, keeping them from firing for a short time. This unit is a must have for air support. Its high hit points and ability to escape quickly give it a very high survivability in combat.
The Sand Dragon's attack rating may not be very high but the splash damage and fairly quick attack rate make it much better than it appears. Attacking quickly makes the Sand Dragon's usefulness vs. infantry because it can keep them off their toes more often. The timonium cost is high so you probably won't be building too many of these. Fortunately, the wealth cost doesn't increase too much with each unit produced so it's a decent choice for spending your timonium while wealth is going elsewhere.