Ajahn Sucitto says, "It may be correct to say that mindfulness is non-judgemental"

https://ajahnsucitto.org/articles/what-is-mindfulness/
excerpt:
But of greater significance in the long run, mindfulness is involved with wisdom. It may be correct to say that mindfulness is non-judgemental – but that doesn’t mean that it doesn’t support assessment. It is in the putting aside self-judgements and short-term impulses (‘covetousness and grief regarding the world’) that an assessment of what is really useful can take place. So to avoid having its attention hijacked, mindfulness has to established and made firm:

I strongly disagree

Sati is about as judgmental as you can get. Think of sati the gatekeeper of the fortress.

• AN 7.67 nagar’-opama
• (7 requisites of fortress)
• (7 requisites leads to 4 types of food )
• (7 requisites of monk)
• (1. saddha/conviction → foundation post )
• (2. hiri/sense-of-shame → moat deep and wide)
• (3. otappa/compunction → encircling road)
• (4. bahu-suto/learned-much dhamma → many weapons stored)
• (5. arraddha-viriya/aroused-vigor → large army stationed)
• (6. sati/mindfulness → wise gatekeeper)
• (7. pañña/discerment → ramparts high and thick)
• (with 7 requisites, 4 jhānas can be obtained easily )
• (1. first jhana → grass, timber, water)
• (2. second jhana → rice, barley)
• (3. third jhana → sesame, green gram, beans)
• (4. fourth jhana → ghee, honey, butter, molasses, salt)

(6. sati/mindfulness → wise gatekeeper)

♦ “seyyathāpi, bhikkhave, rañño paccantime nagare dovāriko hoti paṇḍito byatto medhāvī aññātānaṃ nivāretā ñātānaṃ pavesetā abbhantarānaṃ guttiyā bāhirānaṃ paṭighātāya. evamevaṃ kho, bhikkhave, ariyasāvako satimā hoti paramena satinepakkena samannāgato cirakatampi cirabhāsitampi saritā anussaritā. satidovāriko, bhikkhave, ariyasāvako akusalaṃ pajahati, kusalaṃ bhāveti; sāvajjaṃ pajahati, anavajjaṃ bhāveti; suddhaṃ attānaṃ pariharati. iminā chaṭṭhena saddhammena samannāgato hoti.

“Just as the royal frontier fortress has a gatekeeper—wise, competent, intelligent—to keep out those he doesn’t know and to let in those he does, for the protection of those within and to ward off those without; in the same way a disciple of the noble ones is mindful, endowed with excellent proficiency in mindfulness, remembering & able to call to mind even things that were done & said long ago. With mindfulness as his gatekeeper, the disciple of the noble ones abandons what is unskillful, develops what is skillful, abandons what is blameworthy, develops what is blameless, and looks after himself with purity. With this sixth true quality is he endowed.

You best believe the gatekeeper is judgmental! 

Otherwise all kinds of sweet talking riff raff and defilements wearing clever disguises and using every trick in the book to slip in the fortress. Perhaps Ajahn Sucitto objects to the unnecessary negative emotional component that can accompany someone being hypercritical and judgmental. But being sharply discerning, discriminating, having the intelligence and critical faculty to distinguish the slightest problem, is non-negotiable.  

judg·men·tal

/ˌjəjˈmen(t)l/

adjective

1. of or concerning the use of judgment.

   
   

   "judgmental errors"

   • having or displaying an excessively critical point of view.

     
     

     "I don't like to sound judgmental, but it was a big mistake"

     
     

     synonyms:

     critical, fault-finding, censorious, condemnatory, disapproving, disparaging, deprecating, negative, overcritical, hypercritical, scathing; pass-remarkable "I don't like to sound judgmental but it really was a big mistake" ju·di·cious /jo͞oˈdiSHəs/ adjective having, showing, or done with good judgment or sense. "the efficient and judicious use of pesticides" synonyms: wise, sensible, prudent, politic, shrewd, astute, canny, sagacious, common-sense, commonsensical, sound, well advised, well judged, well thought out, considered, thoughtful, perceptive, discerning, clear-sighted, insightful, far-sighted, percipient, discriminating, informed, intelligent, clever, enlightened, logical, rational;  Do you want a judgmental gatekeeper for Sati Or a sati that is a present moment choiceless awareness zombie? You think he's going to do a good job of keeping the defilements from waltzing through the gate?