A few quotes from the Rabbi on 'Customs of Israel'
in which he rebukes those adhering to a new custom whereby each person recites the blessing alone and so loses benefits
"If they were leading me before a flesh and blood king, who is here today and in the grave tomorrow; if he is angry with me, his anger is not eternal; if he incarcerates me, his incarceration is not an eternal incarceration. If he kills me, his killing is not for eternity [as there is life after any death]. I am able to appease him with words and bribe him with money; even so I would cry. Now that they are leading me before the supreme King of Kings, the Holy One, Blessed be He, Who lives and endures forever and all time; if He is angry with me, His anger is eternal; if He incarcerates me, His incarceration is an eternal incarceration; and if He kills me, His killing is for eternity. I am unable to appease Him with words and bribe him with money. Moreover, but I have two paths before me, one of the Garden of Eden and one of Gehenna, and I do not know on which they are leading me; and will I not cry?"
One is seized by terror as might be a woman giving birth, shaken in horror, especially during these days when the Holy One, blessed be He, sits on the throne of judgement and the entire world passes before Him as might troops… all should reflect on their deeds, and note that their worship of God is insufficient, whether in prayer, Torah study or fulfilling the Commandments. Do not despair of punishment, nor trust that the netherworld be a haven, for all one's deeds are inscribed in the book.
See how the Evil Inclination leads people astray, and can offer no salvation whatsoever: A new evil and bitter custom has appeared. When people now meet to dine and fill their bellies, each person recites the Blessing after Meals alone, losing several benefits: group recitation of the blessing, precision in the recitation, the Amen responses, blessing the host by the guests... This is the custom. A custom of ignoramuses and simpletons. Those who take no pity on themselves and do not revoke this evil custom will discover that they are accountable…
Shlomo Amihud (collected & translated, editor), Pe'ulot Tzaddik, Chapter 18, p. 349, published by Agudat Achim, Jerusalem 1988