things like the barrel(length), handguard its just better quality parts : 810038641669 lower priced specs TROY A3 Pistol (Black) Specifications and Features
TROY Industries Item Number: SPST-CA3-10BT-B1
Semi-Automatic AR15 Pistol
5.56x45 NATO (accepts .223 Remington)
30 Rounds
10" Barrel
Billet Receiver (no forward assist)
9" M-LOK Handguard
A2 Pistol Grip
Pistol Buffer Tube
A2 Flash Hider
Black Anodized Finish
812441028112 higher priced specsTroy Defense A3 Pistol (Matte Black) Specifications and Features:
Troy SPST-CA3-10BT-19
Direct Gas Impingement System
AR-15 Semi Automatic Pistol
5.56 NATO (accepts .223 Remington and 5.56 NATO)
10.5" Barrel
1:7" Right Hand Twist Rate
Forged Aluminum Upper/Lower Receiver
Flat Top Upper
Troy M-LOK BattleRail Free Float (9.25" Length)
Troy Standard Safety Selector
Troy Standard Trigger
Troy Flat Trigger Guard
Troy A2 Control Grip Pistol Grip)
30 Rounds
Troy 30 Round BattleMag (Standard pattern AR-15 Magazine)
A2 Flash Hider
Pistol Buffer Tube/Receiver Extension
Overall Weight 4.2lbs
Hard Coat Anodized Finish
Matte Black

Hi, the more expensive one has Forged Aluminum Upper & Lower Receivers, a Troy M-LOK BattleRail Free Float handguard, and a Troy Flat Trigger Guard.
The other one has a billet receiver, a lesser grade handguard, and a rounded trigger guard.
Basically, the more expensive one has better parts.
Stay safe & have a great day!