I don't have much experience with Mojo::UserAgent, but the Mojo Cookbook has examples for both non-blocking and blocking concurrency. For a simple test I got blocking concurrency with promises working. I built a small test server to avoid any webmaster complaints and easily read and did a little parsing on about 100 fetched URLs per second.

I put a 1 second delay into page delivery and performance seemed to depend on web server configuration. To get good performance I configured for 100 workers restricted to 1 connection each. So with a server named dos-serve-sp.pl I ran:

./dos-serve-sp.pl prefork -w 100 -c 1
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Test server:

#!/usr/bin/env perl

use Modern::Perl;
use Mojolicious::Lite;
use Mojo::UserAgent;

my $ua  = Mojo::UserAgent->new;

# cache page to echo
my $res = $ua->get('www.software-path.com')->result;
if      ($res->is_error)        { say $res->message }
elsif   (not $res->is_success)  {
    die "Unknown response from Mojo::UserAgent"
}
$res->dom->at('head')->append_content(
    '<base href="http://www.software-path.com">'
);

get '/' => sub {
    my ($c) = @_;
    sleep 1;
    $c->render(text => $res->dom->to_string, format => 'html');
};

app->start;
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Test client with blocking concurrency from promises:

#!/usr/bin/env perl

use Modern::Perl;
use Mojo::UserAgent;

my @all_url = ('http://127.0.0.1:3000/') x 200;
my $concurrent_load = 100;

my $ua = Mojo::UserAgent->new;
while (@all_url) {
    my @concurrent_read = map {
        $ua->get_p($_)->then(sub {
            my $tx = shift;
            my $result = $tx->result;
            if ($result->is_success) {
                say $result->dom->at('title')->text
            }
            else {
                say $result->is_error ? $result->message :
                    "Unknown response from Mojo::UserAgent";
            }
        }) # end ->then sub
    } splice @all_url, 0, $concurrent_load;
    Mojo::Promise->all(@concurrent_read)->wait;
}
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