Up to 600m. Even 200m is better than rifle grenades and harder hitting.
https://en.wikipedia.org/wiki/Rifle_grenade#Comparison_of_performance
I think an error was made during translation. The Japanese wikipedia page actually states:
1) 670m was the range for Type 10/Type91 800 gram fragmentation grenades (these can be launched also from older Type 10 launcher)
2) Later in the war, winged version of Type 91 increased the range to 800m
3) 200m was the range of heavy Type 89 HE bomb (1.46kg). Type 89 bomb was actually designed to match Type 92 Battalion Gun 70mm shell explosive strength to give a kill radius 10m.
The usage of light and heavy shells was different, of course. Light grenades to kill enemy infantry in open while heavy bombs are mostly against MG pillboxes. Actually, Japanese loved anti-pillbox mortar concept very much. Their 50mm combat engineer mortar (Type 98) were capable to hurl a 4.5kg bomb (larger than 8 cm Granatwerfer 34).
About operational effectiveness of Japanese Type 89 launcher:
*poor in OTL
*would be average if enough ammunition supplied
*would be very good if enough ammunition and a means to carry it are supplied
Japanese claimed to pick-off an US MG team at maximal range from first shot. Unfortunately, usually each launcher was supplied only with 8 light grenades. Heavy bombs were issued on special occasion. So given explosive filling of each grenade 0.3kg, low-caliber multiplier of 10 and basic high-angle fire efficiency 8 KIA/ton, the IJA division with 332 Type 89 launchers will be able to kill 0.0003*10*8*8*332=65 US or Chinese soldiers. Counting wounded, Japanese soldier with Type 89 launcher defending in ideal conditions can inflict to enemy 1:1 casualty before running out of ammunition. Actually, if rate of fire 25 rounds/minute can be sustained (need a reloader for this), and 2-line advance of US troops with average speed 1.5 m/s it would be most efficient to supply each launcher with 125 grenades to run out of ammo just before being overrun. But Japanese simply were not able to produce so much ammunition.. Also, if so much grenades were available, the team to carry and fire it will most likely include 8 men (Artillerist, reloader, reserve artillerist, reserve reloader, 4 ammunition porters). If such teams would be possible, the casualties ratio can be 2:1 in favour of Japanese.
So, conclusion: Japanese should have at least a motorbike (to carry ammunition) for each Type 89 launcher to be efficient. But given the pitiful state of their auto-mobile industry (as well as ammunition industry), it was plainly impossible.
Returning to original question: how about German Motorcycle Battalions in Europe armed with something like Type 89 mortar? They can roll off-road, smash light Soviet fortifications and hold it against 10-times amount of light infantry.