Deconstructing the 3.8-Star Pool Robot: The Nu Cobalt 731-i's "Value vs. Risk" Gamble

In the $400 price range, the robotic pool cleaner market is a high-stakes gamble. You are looking for a “value” product that performs like a $1,000 machine, but you risk getting a “dud” that fails after a month.

The Nu Cobalt 731-i is a perfect case study in this gamble. It’s a corded, wall-climbing robot with a highly polarized 3.8-star rating from 64 reviews. On one hand, 59% of users give it 5 stars, calling it “fantastic” and “way better than ALL the others.” On the other, a massive 23% of users give it 1 star, calling it a “defective unit” with “no response” from the company.

This is not a review. This is a deconstruction of that 3.8-star paradox. We’ll analyze the “5-star promise” (the specs) versus the “1-star reality” (the user-reported failures).

The “5-Star Promise”: Deconstructing the Specs

The 5-star reviews are from users who “won” the lottery. They received a fully functional unit and are thrilled with the performance for the price. The specs they are praising are clear.

1. Corded Power with “NO-TWIST” Swivel:
Unlike cordless models that rely on a battery (which is often the first part to fail), the 731-i is a corded electric model. This means consistent, reliable power for its 2-hour cleaning cycle. Its critical feature is the 50-foot power cord with a “NO-TWIST swivel.” This is an engineering solution to the #1 problem of corded bots: tangling. As 5-star user “Christopher” notes, “The cord is on swivels so it never gets tangled or obstructs the unit from cleaning.”

2. Direct-Drive Motor and Wall Climbing:
The robot is a true “wall climber,” a feature often missing on budget units. It uses a direct-drive motor for “greater traction.” This provides the torque needed to climb vertical walls and scrub the waterline. * User “Christopher” (5-star): “climbs right up the walls to the waterline before reversing back down.” * User “Jeff” (5-star): “Climbs the walls up just past the water line where you can hear and see the suction power.”

3. The “Pleated” Filter Bag:
This is the product’s most unique feature. It doesn’t use a simple mesh basket. It uses an “extra-large pleated filter bag.” User “John He” (5-star) identified this as the key:

“It uses a very unusual filter bag like the dust collector I used in my hobby wood shop. Surprising it works great to pick up dirt and fine filtration… Very fine dirt trapped by this pleated filter. I think the filter construction is the key.”

This “pleated” design (like a car’s air filter) dramatically increases the surface area, allowing it to trap fine silt, sand, and algae (“LoyalFriend” - 5 star) without immediately clogging. User “Christopher” confirms it “comes with a fine sediment filter and also a filter for large debris.”

The “1-Star Reality”: Deconstructing the 3.8-Star Gamble

The “5-star promise” is clear: it’s a “tank” (as “Christopher” said) that cleans walls and filters fine dirt for a great price. So, why do 23% of buyers give it 1 star?

The 1-star reviews are not “mixed opinions.” They are reports of catastrophic, out-of-the-box failure.

Risk 1: The “Dead on Arrival” (DOA) Lottery * User “Yggi” (1-star): “Looks very good! Seems to be good quality for the money. But do d not even start.”

Risk 2: The “Early Death” Failure * User “TBiggs” (1-star): “Fast forward about 8 weeks… plugged it in to charge it and instead of the light… it started making a grinding sound which would not stop.” * User “Pat F.” (Original 1-star review): “worked fine for 2 days, but on day 3… the rubber wheel/track has come off… I obviously got a defective unit.”

These reviews indicate a significant Quality Control (QC) problem. You are gambling that you will not receive a “defective unit.”

Risk 3: The Real Gamble — The Warranty
This is the most critical insight from the 1-star reviews. A defective unit is bad. A defective unit with no customer support is a $400 paperweight.

User “Amazon Customer” (“Michael”) (1-star):

“Company Does Not Honor their warranty. I HAVE ATTEMPTED TO CALL …. UNAVAILABLE NUMBER. INHAVE MADE SEVERAL EMAILS.. NO RESPONSE… Yesterday the power supply just stop sending power… Please honor your product warranty.”

This is the ultimate risk. However, it’s contradicted by “Pat F.,” who updated their review to 5 stars, stating:

“UPDATE: great customer support! After filing a warranty claim… they contacted me, replaced the Winny [sic] with a new one that is working as expected.”

Conclusion: A High-Risk, High-Reward Value Prop

The Nu Cobalt 731-i is a case study in the 3.8-star paradox. It is not a “bad” product. It is a high-risk one.

The 5-star (59%) majority confirms its design is excellent. It offers wall-climbing and superior filtration at a price that “is comparable with units twice it’s cost” (“Rex G. Kunz”).

The 1-star (23%) minority confirms its manufacturing and support are a gamble. You risk receiving a “lemon,” and if you do, you further risk entering a customer-support void.

It is, as 4-star user “Customer” put it, a “Great product for the value… This robotic pool cleaner works just as well as a $1000 dollar robot. Only difference is the $1000 dollar robot has more durabilty.”