I think the personality (nature) of people determines the form of their attachment with bhagawan.

Some do not have anything ask for and remain attached with him eternally (like nityasuris, muktAtmAs)

Some remain attached to Brahmam through Bhakti/Gyana yogam.

Yantram based faith is also an accepted form of worship, provided the user realises that the ‘Yantram’ doesn’t control Bhagawan but Bhagawan wishes to be controlled by it just for the sake of bhakta. The moment somebody starts thinking the other way, it will lose its purpose and value.

But Velukkudi swami has told in a few discourses that creation of a true ‘Yantram’ is not an ordinary task. It requires a lot of shraddhai and kramam to be followed without any deviation.  Only then it will give the required phalan. Very few people have that shraddhai today to make a true ‘Yantram’; so for all practical purposes (unless we believe in its source) it is better to avoid it.

-Adiyen

I don’t think ‘Shalagramam’ is a yantram because it is naturally available in river ‘Gandaki’.

Srimathe Rangaramanuja Mahadesikaya Namaha
Srimathe SriVarAha MahAdEsikAya Namaha

Sri Velukkudi Krishnan Swamy Thiruvadigaley Sharanam

Dhanyosmi Swami

Let’s not be surprised if people print yantrams on 3D printers.
Dasanudasan