It's been a little over a month...
I replaced all the strings with Aquila strings for a 415 tuning. Now the instrument is stable although it's still very fresh. The sound with the new strings is truly beautiful. As others have noted, it's surprising for such a low-priced instrument. The weak point is the bass pegbox. The strings are too tilted with angles that make it difficult to hold and tune the V, VI, VII, and VIII drone bass strings. I solved the problem by drilling out the VI, VII, and VIII pegs on the outside of the box. However, the position of the V drone is extremely awkward, both for securing the string to the peg if it needs changing (unless you remove all the other strings). Furthermore, when tuning, the peg can touch the neighboring one, preventing either from turning easily, which is truly impractical. It may seem like a minor issue, but in concert, you don't want to find yourself with a stuck tuning peg if you need to quickly adjust the tuning, which is already a uneasy task with the drones.
Because of this, I was hesitant to confirm the 4-star rating for quality. However, overall, the instrument is well-made, solid, carefully finished. I would still recommend it to anyone who wants to learn the instrument's specific repertoire and the practice of basso continuo.