Hello 720digital,
Thank you for your interest about our extension.
For client-side validation you have to enable this in module configuration and add "css" class 'validate-vat' to each field that should be validated. We did not integrate of automatically adding the validate class to the field, because there is many designs and each one can place it everywhere.
For example for the account page edit file base/defualt/template/customer/widget/taxvat.phtml
from
<label for="<?php echo $this->getFieldId('taxvat')?>"<?php if ($this->isRequired()) echo ' class="required"' ?>><?php if ($this->isRequired()) echo '<em>*</em>' ?><?php echo $this->__('Tax/VAT number') ?></label>
<div class="input-box">
<input type="text" id="<?php echo $this->getFieldId('taxvat')?>" name="<?php echo $this->getFieldName('taxvat')?>" value="<?php echo $this->escapeHtml($this->getTaxvat()) ?>" title="<?php echo $this->__('Tax/VAT number') ?>" class="input-text <?php echo $this->helper('customer/address')->getAttributeValidationClass('taxvat') ?>" <?php echo $this->getFieldParams() ?> />
</div>
to
<label for="<?php echo $this->getFieldId('taxvat')?>"<?php if ($this->isRequired()) echo ' class="required"' ?>><?php if ($this->isRequired()) echo '<em>*</em>' ?><?php echo $this->__('Tax/VAT number') ?></label>
<div class="input-box">
<input type="text" id="<?php echo $this->getFieldId('taxvat')?>" name="<?php echo $this->getFieldName('taxvat')?>" value="<?php echo $this->escapeHtml($this->getTaxvat()) ?>" title="<?php echo $this->__('Tax/VAT number') ?>" class="input-text validate-vat <?php echo $this->helper('customer/address')->getAttributeValidationClass('taxvat') ?>" <?php echo $this->getFieldParams() ?> />
</div>
